"Buttery Smooth" Tab Capture.

content/browser/media/capture/video_capture_oracle_unittest.cc

 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/browser/media/capture/video_capture_oracle.h"
 
+#include <cstdlib>
+#include <utility>
+#include <vector>
+
+#include "base/logging.h"
 #include "base/strings/stringprintf.h"
 #include "base/time/time.h"
 #include "testing/gtest/include/gtest/gtest.h"
+#include "ui/gfx/geometry/rect.h"
 
 namespace content {
 namespace {
 
+bool AddEventAndConsiderSampling(SmoothEventSampler* sampler,
+                                 base::TimeTicks event_time) {
+  sampler->ConsiderPresentationEvent(event_time);
+  return sampler->ShouldSample();
+}
+
 void SteadyStateSampleAndAdvance(base::TimeDelta vsync,
                                  SmoothEventSampler* sampler,
                                  base::TimeTicks* t) {
-  ASSERT_TRUE(sampler->AddEventAndConsiderSampling(*t));
+  ASSERT_TRUE(AddEventAndConsiderSampling(sampler, *t));
   ASSERT_TRUE(sampler->HasUnrecordedEvent());
   sampler->RecordSample();
   ASSERT_FALSE(sampler->HasUnrecordedEvent());
   ASSERT_FALSE(sampler->IsOverdueForSamplingAt(*t));
   *t += vsync;
   ASSERT_FALSE(sampler->IsOverdueForSamplingAt(*t));
 }
 
 void SteadyStateNoSampleAndAdvance(base::TimeDelta vsync,
                                    SmoothEventSampler* sampler,
                                    base::TimeTicks* t) {
-  ASSERT_FALSE(sampler->AddEventAndConsiderSampling(*t));
+  ASSERT_FALSE(AddEventAndConsiderSampling(sampler, *t));
   ASSERT_TRUE(sampler->HasUnrecordedEvent());
   ASSERT_FALSE(sampler->IsOverdueForSamplingAt(*t));
   *t += vsync;
   ASSERT_FALSE(sampler->IsOverdueForSamplingAt(*t));
 }
 
-void TimeTicksFromString(const char* string, base::TimeTicks* t) {
-  base::Time time;
-  ASSERT_TRUE(base::Time::FromString(string, &time));
-  *t = base::TimeTicks::UnixEpoch() + (time - base::Time::UnixEpoch());
+base::TimeTicks InitialTestTimeTicks() {
+  return base::TimeTicks() + base::TimeDelta::FromSeconds(1);
 }
 
 void TestRedundantCaptureStrategy(base::TimeDelta capture_period,
                                   int redundant_capture_goal,
                                   SmoothEventSampler* sampler,
                                   base::TimeTicks* t) {
   // Before any events have been considered, we're overdue for sampling.
   ASSERT_TRUE(sampler->IsOverdueForSamplingAt(*t));
 
   // Consider the first event.  We want to sample that.
   ASSERT_FALSE(sampler->HasUnrecordedEvent());
-  ASSERT_TRUE(sampler->AddEventAndConsiderSampling(*t));
+  ASSERT_TRUE(AddEventAndConsiderSampling(sampler, *t));
   ASSERT_TRUE(sampler->HasUnrecordedEvent());
   sampler->RecordSample();
   ASSERT_FALSE(sampler->HasUnrecordedEvent());
 
-  // After more than one capture period has passed without considering an event,
-  // we should repeatedly be overdue for sampling.  However, once the redundant
-  // capture goal is achieved, we should no longer be overdue for sampling.
-  *t += capture_period * 4;
+  // After more than 250 ms has passed without considering an event, we should
+  // repeatedly be overdue for sampling.  However, once the redundant capture
+  // goal is achieved, we should no longer be overdue for sampling.
+  *t += base::TimeDelta::FromMilliseconds(250);
   for (int i = 0; i < redundant_capture_goal; i++) {
     SCOPED_TRACE(base::StringPrintf("Iteration %d", i));
     ASSERT_FALSE(sampler->HasUnrecordedEvent());
     ASSERT_TRUE(sampler->IsOverdueForSamplingAt(*t))
         << "Should sample until redundant capture goal is hit";
     sampler->RecordSample();
     *t += capture_period;  // Timer fires once every capture period.
   }
   ASSERT_FALSE(sampler->IsOverdueForSamplingAt(*t))
       << "Should not be overdue once redundant capture goal achieved.";
 }
 
+}  // namespace
+
 // 60Hz sampled at 30Hz should produce 30Hz.  In addition, this test contains
 // much more comprehensive before/after/edge-case scenarios than the others.
 TEST(SmoothEventSamplerTest, Sample60HertzAt30Hertz) {
   const base::TimeDelta capture_period = base::TimeDelta::FromSeconds(1) / 30;
   const int redundant_capture_goal = 200;
   const base::TimeDelta vsync = base::TimeDelta::FromSeconds(1) / 60;
 
   SmoothEventSampler sampler(capture_period, true, redundant_capture_goal);
-  base::TimeTicks t;
-  TimeTicksFromString("Sat, 23 Mar 2013 1:21:08 GMT", &t);
+  base::TimeTicks t = InitialTestTimeTicks();
 
   TestRedundantCaptureStrategy(capture_period, redundant_capture_goal,
                                &sampler, &t);
 
   // Steady state, we should capture every other vsync, indefinitely.
   for (int i = 0; i < 100; i++) {
     SCOPED_TRACE(base::StringPrintf("Iteration %d", i));
     SteadyStateSampleAndAdvance(vsync, &sampler, &t);
     SteadyStateNoSampleAndAdvance(vsync, &sampler, &t);
   }
 
   // Now pretend we're limited by backpressure in the pipeline. In this scenario
   // case we are adding events but not sampling them.
   for (int i = 0; i < 20; i++) {
     SCOPED_TRACE(base::StringPrintf("Iteration %d", i));
-    ASSERT_EQ(i >= 7, sampler.IsOverdueForSamplingAt(t));
-    ASSERT_TRUE(sampler.AddEventAndConsiderSampling(t));
+    ASSERT_EQ(i >= 14, sampler.IsOverdueForSamplingAt(t));
+    ASSERT_TRUE(AddEventAndConsiderSampling(&sampler, t));
     ASSERT_TRUE(sampler.HasUnrecordedEvent());
     t += vsync;
   }
 
   // Now suppose we can sample again. We should be back in the steady state,
   // but at a different phase.
   ASSERT_TRUE(sampler.IsOverdueForSamplingAt(t));
   for (int i = 0; i < 100; i++) {
     SCOPED_TRACE(base::StringPrintf("Iteration %d", i));
     SteadyStateSampleAndAdvance(vsync, &sampler, &t);
     SteadyStateNoSampleAndAdvance(vsync, &sampler, &t);
   }
 }
 
 // 50Hz sampled at 30Hz should produce a sequence where some frames are skipped.
 TEST(SmoothEventSamplerTest, Sample50HertzAt30Hertz) {
   const base::TimeDelta capture_period = base::TimeDelta::FromSeconds(1) / 30;
   const int redundant_capture_goal = 2;
   const base::TimeDelta vsync = base::TimeDelta::FromSeconds(1) / 50;
 
   SmoothEventSampler sampler(capture_period, true, redundant_capture_goal);
-  base::TimeTicks t;
-  TimeTicksFromString("Sat, 23 Mar 2013 1:21:08 GMT", &t);
+  base::TimeTicks t = InitialTestTimeTicks();
 
   TestRedundantCaptureStrategy(capture_period, redundant_capture_goal,
                                &sampler, &t);
 
   // Steady state, we should capture 1st, 2nd and 4th frames out of every five
   // frames, indefinitely.
   for (int i = 0; i < 100; i++) {
     SCOPED_TRACE(base::StringPrintf("Iteration %d", i));
     SteadyStateSampleAndAdvance(vsync, &sampler, &t);
     SteadyStateSampleAndAdvance(vsync, &sampler, &t);
     SteadyStateNoSampleAndAdvance(vsync, &sampler, &t);
     SteadyStateSampleAndAdvance(vsync, &sampler, &t);
     SteadyStateNoSampleAndAdvance(vsync, &sampler, &t);
   }
 
   // Now pretend we're limited by backpressure in the pipeline. In this scenario
   // case we are adding events but not sampling them.
-  for (int i = 0; i < 12; i++) {
+  for (int i = 0; i < 20; i++) {
     SCOPED_TRACE(base::StringPrintf("Iteration %d", i));
-    ASSERT_EQ(i >= 5, sampler.IsOverdueForSamplingAt(t));
-    ASSERT_TRUE(sampler.AddEventAndConsiderSampling(t));
+    ASSERT_EQ(i >= 11, sampler.IsOverdueForSamplingAt(t));
+    ASSERT_TRUE(AddEventAndConsiderSampling(&sampler, t));
     t += vsync;
   }
 
   // Now suppose we can sample again. We should be back in the steady state
   // again.
   ASSERT_TRUE(sampler.IsOverdueForSamplingAt(t));
   for (int i = 0; i < 100; i++) {
     SCOPED_TRACE(base::StringPrintf("Iteration %d", i));
     SteadyStateSampleAndAdvance(vsync, &sampler, &t);
     SteadyStateSampleAndAdvance(vsync, &sampler, &t);
     SteadyStateNoSampleAndAdvance(vsync, &sampler, &t);
     SteadyStateSampleAndAdvance(vsync, &sampler, &t);
     SteadyStateNoSampleAndAdvance(vsync, &sampler, &t);
   }
 }
 
 // 75Hz sampled at 30Hz should produce a sequence where some frames are skipped.
 TEST(SmoothEventSamplerTest, Sample75HertzAt30Hertz) {
   const base::TimeDelta capture_period = base::TimeDelta::FromSeconds(1) / 30;
   const int redundant_capture_goal = 32;
   const base::TimeDelta vsync = base::TimeDelta::FromSeconds(1) / 75;
 
   SmoothEventSampler sampler(capture_period, true, redundant_capture_goal);
-  base::TimeTicks t;
-  TimeTicksFromString("Sat, 23 Mar 2013 1:21:08 GMT", &t);
+  base::TimeTicks t = InitialTestTimeTicks();
 
   TestRedundantCaptureStrategy(capture_period, redundant_capture_goal,
                                &sampler, &t);
 
   // Steady state, we should capture 1st and 3rd frames out of every five
   // frames, indefinitely.
   SteadyStateSampleAndAdvance(vsync, &sampler, &t);
   SteadyStateNoSampleAndAdvance(vsync, &sampler, &t);
   for (int i = 0; i < 100; i++) {
     SCOPED_TRACE(base::StringPrintf("Iteration %d", i));
     SteadyStateSampleAndAdvance(vsync, &sampler, &t);
     SteadyStateNoSampleAndAdvance(vsync, &sampler, &t);
     SteadyStateSampleAndAdvance(vsync, &sampler, &t);
     SteadyStateNoSampleAndAdvance(vsync, &sampler, &t);
     SteadyStateNoSampleAndAdvance(vsync, &sampler, &t);
   }
 
   // Now pretend we're limited by backpressure in the pipeline. In this scenario
   // case we are adding events but not sampling them.
   for (int i = 0; i < 20; i++) {
     SCOPED_TRACE(base::StringPrintf("Iteration %d", i));
-    ASSERT_EQ(i >= 8, sampler.IsOverdueForSamplingAt(t));
-    ASSERT_TRUE(sampler.AddEventAndConsiderSampling(t));
+    ASSERT_EQ(i >= 16, sampler.IsOverdueForSamplingAt(t));
+    ASSERT_TRUE(AddEventAndConsiderSampling(&sampler, t));
     t += vsync;
   }
 
   // Now suppose we can sample again. We capture the next frame, and not the one
   // after that, and then we're back in the steady state again.
   ASSERT_TRUE(sampler.IsOverdueForSamplingAt(t));
   SteadyStateSampleAndAdvance(vsync, &sampler, &t);
   SteadyStateNoSampleAndAdvance(vsync, &sampler, &t);
   for (int i = 0; i < 100; i++) {
     SCOPED_TRACE(base::StringPrintf("Iteration %d", i));
     SteadyStateSampleAndAdvance(vsync, &sampler, &t);
     SteadyStateNoSampleAndAdvance(vsync, &sampler, &t);
     SteadyStateSampleAndAdvance(vsync, &sampler, &t);
     SteadyStateNoSampleAndAdvance(vsync, &sampler, &t);
     SteadyStateNoSampleAndAdvance(vsync, &sampler, &t);
   }
 }
 
 // 30Hz sampled at 30Hz should produce 30Hz.
 TEST(SmoothEventSamplerTest, Sample30HertzAt30Hertz) {
   const base::TimeDelta capture_period = base::TimeDelta::FromSeconds(1) / 30;
   const int redundant_capture_goal = 1;
   const base::TimeDelta vsync = base::TimeDelta::FromSeconds(1) / 30;
 
   SmoothEventSampler sampler(capture_period, true, redundant_capture_goal);
-  base::TimeTicks t;
-  TimeTicksFromString("Sat, 23 Mar 2013 1:21:08 GMT", &t);
+  base::TimeTicks t = InitialTestTimeTicks();
 
   TestRedundantCaptureStrategy(capture_period, redundant_capture_goal,
                                &sampler, &t);
 
   // Steady state, we should capture every vsync, indefinitely.
   for (int i = 0; i < 200; i++) {
     SCOPED_TRACE(base::StringPrintf("Iteration %d", i));
     SteadyStateSampleAndAdvance(vsync, &sampler, &t);
   }
 
   // Now pretend we're limited by backpressure in the pipeline. In this scenario
   // case we are adding events but not sampling them.
-  for (int i = 0; i < 7; i++) {
+  for (int i = 0; i < 10; i++) {
     SCOPED_TRACE(base::StringPrintf("Iteration %d", i));
-    ASSERT_EQ(i >= 3, sampler.IsOverdueForSamplingAt(t));
-    ASSERT_TRUE(sampler.AddEventAndConsiderSampling(t));
+    ASSERT_EQ(i >= 7, sampler.IsOverdueForSamplingAt(t));
+    ASSERT_TRUE(AddEventAndConsiderSampling(&sampler, t));
     t += vsync;
   }
 
   // Now suppose we can sample again. We should be back in the steady state.
   ASSERT_TRUE(sampler.IsOverdueForSamplingAt(t));
   for (int i = 0; i < 100; i++) {
     SCOPED_TRACE(base::StringPrintf("Iteration %d", i));
     SteadyStateSampleAndAdvance(vsync, &sampler, &t);
   }
 }
 
 // 24Hz sampled at 30Hz should produce 24Hz.
 TEST(SmoothEventSamplerTest, Sample24HertzAt30Hertz) {
   const base::TimeDelta capture_period = base::TimeDelta::FromSeconds(1) / 30;
   const int redundant_capture_goal = 333;
   const base::TimeDelta vsync = base::TimeDelta::FromSeconds(1) / 24;
 
   SmoothEventSampler sampler(capture_period, true, redundant_capture_goal);
-  base::TimeTicks t;
-  TimeTicksFromString("Sat, 23 Mar 2013 1:21:08 GMT", &t);
+  base::TimeTicks t = InitialTestTimeTicks();
 
   TestRedundantCaptureStrategy(capture_period, redundant_capture_goal,
                                &sampler, &t);
 
   // Steady state, we should capture every vsync, indefinitely.
   for (int i = 0; i < 200; i++) {
     SCOPED_TRACE(base::StringPrintf("Iteration %d", i));
     SteadyStateSampleAndAdvance(vsync, &sampler, &t);
   }
 
   // Now pretend we're limited by backpressure in the pipeline. In this scenario
   // case we are adding events but not sampling them.
-  for (int i = 0; i < 7; i++) {
+  for (int i = 0; i < 10; i++) {
     SCOPED_TRACE(base::StringPrintf("Iteration %d", i));
-    ASSERT_EQ(i >= 3, sampler.IsOverdueForSamplingAt(t));
-    ASSERT_TRUE(sampler.AddEventAndConsiderSampling(t));
+    ASSERT_EQ(i >= 6, sampler.IsOverdueForSamplingAt(t));
+    ASSERT_TRUE(AddEventAndConsiderSampling(&sampler, t));
     t += vsync;
   }
 
   // Now suppose we can sample again. We should be back in the steady state.
   ASSERT_TRUE(sampler.IsOverdueForSamplingAt(t));
   for (int i = 0; i < 100; i++) {
     SCOPED_TRACE(base::StringPrintf("Iteration %d", i));
     SteadyStateSampleAndAdvance(vsync, &sampler, &t);
   }
 }
 
 TEST(SmoothEventSamplerTest, DoubleDrawAtOneTimeStillDirties) {
   const base::TimeDelta capture_period = base::TimeDelta::FromSeconds(1) / 30;
   const base::TimeDelta overdue_period = base::TimeDelta::FromSeconds(1);
 
   SmoothEventSampler sampler(capture_period, true, 1);
-  base::TimeTicks t;
-  TimeTicksFromString("Sat, 23 Mar 2013 1:21:08 GMT", &t);
+  base::TimeTicks t = InitialTestTimeTicks();
 
-  ASSERT_TRUE(sampler.AddEventAndConsiderSampling(t));
+  ASSERT_TRUE(AddEventAndConsiderSampling(&sampler, t));
   sampler.RecordSample();
   ASSERT_FALSE(sampler.IsOverdueForSamplingAt(t))
       << "Sampled last event; should not be dirty.";
   t += overdue_period;
 
   // Now simulate 2 events with the same clock value.
-  ASSERT_TRUE(sampler.AddEventAndConsiderSampling(t));
+  ASSERT_TRUE(AddEventAndConsiderSampling(&sampler, t));
   sampler.RecordSample();
-  ASSERT_FALSE(sampler.AddEventAndConsiderSampling(t))
+  ASSERT_FALSE(AddEventAndConsiderSampling(&sampler, t))
       << "Two events at same time -- expected second not to be sampled.";
   ASSERT_TRUE(sampler.IsOverdueForSamplingAt(t + overdue_period))
       << "Second event should dirty the capture state.";
   sampler.RecordSample();
   ASSERT_FALSE(sampler.IsOverdueForSamplingAt(t + overdue_period));
 }
 
 TEST(SmoothEventSamplerTest, FallbackToPollingIfUpdatesUnreliable) {
   const base::TimeDelta timer_interval = base::TimeDelta::FromSeconds(1) / 30;
 
   SmoothEventSampler should_not_poll(timer_interval, true, 1);
   SmoothEventSampler should_poll(timer_interval, false, 1);
-  base::TimeTicks t;
-  TimeTicksFromString("Sat, 23 Mar 2013 1:21:08 GMT", &t);
+  base::TimeTicks t = InitialTestTimeTicks();
 
   // Do one round of the "happy case" where an event was received and
   // RecordSample() was called by the client.
-  ASSERT_TRUE(should_not_poll.AddEventAndConsiderSampling(t));
-  ASSERT_TRUE(should_poll.AddEventAndConsiderSampling(t));
+  ASSERT_TRUE(AddEventAndConsiderSampling(&should_not_poll, t));
+  ASSERT_TRUE(AddEventAndConsiderSampling(&should_poll, t));
   should_not_poll.RecordSample();
   should_poll.RecordSample();
 
-  // One time period ahead, neither sampler says we're overdue.
-  for (int i = 0; i < 3; i++) {
+  // For the following time period, before 250 ms has elapsed, neither sampler
+  // says we're overdue.
+  const int non_overdue_intervals = static_cast<int>(
+      base::TimeDelta::FromMilliseconds(250) / timer_interval);
+  for (int i = 0; i < non_overdue_intervals; i++) {
     t += timer_interval;
     ASSERT_FALSE(should_not_poll.IsOverdueForSamplingAt(t))
         << "Sampled last event; should not be dirty.";
     ASSERT_FALSE(should_poll.IsOverdueForSamplingAt(t))
         << "Dirty interval has not elapsed yet.";
   }
 
   // Next time period ahead, both samplers say we're overdue.  The non-polling
   // sampler is returning true here because it has been configured to allow one
   // redundant capture.
-  t += timer_interval;
+  t += timer_interval;  // Step past the 250 ms threshold.
   ASSERT_TRUE(should_not_poll.IsOverdueForSamplingAt(t))
       << "Sampled last event; is dirty one time only to meet redundancy goal.";
   ASSERT_TRUE(should_poll.IsOverdueForSamplingAt(t))
       << "If updates are unreliable, must fall back to polling when idle.";
   should_not_poll.RecordSample();
   should_poll.RecordSample();
 
   // Forever more, the non-polling sampler returns false while the polling one
   // returns true.
   for (int i = 0; i < 100; ++i) {
     t += timer_interval;
     ASSERT_FALSE(should_not_poll.IsOverdueForSamplingAt(t))
         << "Sampled last event; should not be dirty.";
     ASSERT_TRUE(should_poll.IsOverdueForSamplingAt(t))
         << "If updates are unreliable, must fall back to polling when idle.";
     should_poll.RecordSample();
   }
   t += timer_interval / 3;
   ASSERT_FALSE(should_not_poll.IsOverdueForSamplingAt(t))
       << "Sampled last event; should not be dirty.";
   ASSERT_TRUE(should_poll.IsOverdueForSamplingAt(t))
       << "If updates are unreliable, must fall back to polling when idle.";
   should_poll.RecordSample();
 }
 
+namespace {
+
 struct DataPoint {
   bool should_capture;
   double increment_ms;
 };
 
 void ReplayCheckingSamplerDecisions(const DataPoint* data_points,
                                     size_t num_data_points,
                                     SmoothEventSampler* sampler) {
-  base::TimeTicks t;
-  TimeTicksFromString("Sat, 23 Mar 2013 1:21:08 GMT", &t);
+  base::TimeTicks t = InitialTestTimeTicks();
   for (size_t i = 0; i < num_data_points; ++i) {
     t += base::TimeDelta::FromMicroseconds(
         static_cast<int64>(data_points[i].increment_ms * 1000));
     ASSERT_EQ(data_points[i].should_capture,
-              sampler->AddEventAndConsiderSampling(t))
+              AddEventAndConsiderSampling(sampler, t))
         << "at data_points[" << i << ']';
     if (data_points[i].should_capture)
       sampler->RecordSample();
   }
 }
 
+}  // namespace
+
 TEST(SmoothEventSamplerTest, DrawingAt24FpsWith60HzVsyncSampledAt30Hertz) {
   // Actual capturing of timing data: Initial instability as a 24 FPS video was
   // started from a still screen, then clearly followed by steady-state.
   static const DataPoint data_points[] = {
     { true, 1437.93 }, { true, 150.484 }, { true, 217.362 }, { true, 50.161 },
     { true, 33.44 }, { false, 0 }, { true, 16.721 }, { true, 66.88 },
     { true, 50.161 }, { false, 0 }, { false, 0 }, { true, 50.16 },
     { true, 33.441 }, { true, 16.72 }, { false, 16.72 }, { true, 117.041 },
     { true, 16.72 }, { false, 16.72 }, { true, 50.161 }, { true, 50.16 },
     { true, 33.441 }, { true, 33.44 }, { true, 33.44 }, { true, 16.72 },
@@ skipping 86 matching lines @@
     { true, 33.441 }, { false, 0 }, { true, 33.44 }, { false, 16.72 },
     { true, 33.44 }, { false, 0 }, { true, 16.721 }, { true, 50.161 },
     { false, 0 }, { true, 16.72 }, { true, 33.44 }, { false, 0 },
     { true, 33.441 }, { false, 16.72 }, { true, 16.72 }, { true, 50.16 }
   };
 
   SmoothEventSampler sampler(base::TimeDelta::FromSeconds(1) / 30, true, 3);
   ReplayCheckingSamplerDecisions(data_points, arraysize(data_points), &sampler);
 }
 
+class AnimatedContentSamplerTest : public ::testing::Test {
+ public:
+  AnimatedContentSamplerTest() {}
+  virtual ~AnimatedContentSamplerTest() {}
+
+  virtual void SetUp() OVERRIDE {
+    const base::TimeDelta since_epoch =
+        InitialTestTimeTicks() - base::TimeTicks::UnixEpoch();
+    rand_seed_ = abs(static_cast<int>(since_epoch.InMicroseconds()));
+    sampler_.reset(new AnimatedContentSampler(GetMinCapturePeriod()));
+  }
+
+ protected:
+  // Overridden by subclass for parameterized tests.
+  virtual base::TimeDelta GetMinCapturePeriod() const {
+    return base::TimeDelta::FromSeconds(1) / 30;
+  }
+
+  AnimatedContentSampler* sampler() const {
+    return sampler_.get();
+  }
+
+  int GetRandomInRange(int begin, int end) {
+    const int len = end - begin;
+    const int rand_offset = (len == 0) ? 0 : (NextRandomInt() % (end - begin));
+    return begin + rand_offset;
+  }
+
+  gfx::Rect GetRandomDamageRect() {
+    return gfx::Rect(0, 0, GetRandomInRange(1, 100), GetRandomInRange(1, 100));
+  }
+
+  gfx::Rect GetContentDamageRect() {
+    // This must be distinct from anything GetRandomDamageRect() could return.
+    return gfx::Rect(0, 0, 1280, 720);
+  }
+
+  // Directly inject an observation.  Only used to test
+  // ElectMajorityDamageRect().
+  void ObserveDamageRect(const gfx::Rect& damage_rect) {
+    sampler_->observations_.push_back(
+        AnimatedContentSampler::Observation(damage_rect, base::TimeTicks()));
+  }
+
+  gfx::Rect ElectMajorityDamageRect() const {
+    return sampler_->ElectMajorityDamageRect();
+  }
+
+ private:
+  // Note: Not using base::RandInt() because it is horribly slow on debug
+  // builds.  The following is a very simple, deterministic LCG:
+  int NextRandomInt() {
+    rand_seed_ = (1103515245 * rand_seed_ + 12345) % (1 << 31);
+    return rand_seed_;
+  }
+
+  int rand_seed_;
+  scoped_ptr<AnimatedContentSampler> sampler_;
+};
+
+TEST_F(AnimatedContentSamplerTest, ElectsNoneFromZeroDamageRects) {
+  EXPECT_EQ(gfx::Rect(), ElectMajorityDamageRect());
+}
+
+TEST_F(AnimatedContentSamplerTest, ElectsMajorityFromOneDamageRect) {
+  const gfx::Rect the_one_rect(0, 0, 1, 1);
+  ObserveDamageRect(the_one_rect);
+  EXPECT_EQ(the_one_rect, ElectMajorityDamageRect());
+}
+
+TEST_F(AnimatedContentSamplerTest, ElectsNoneFromTwoDamageRectsOfSameArea) {
+  const gfx::Rect one_rect(0, 0, 1, 1);
+  const gfx::Rect another_rect(1, 1, 1, 1);
+  ObserveDamageRect(one_rect);
+  ObserveDamageRect(another_rect);
+  EXPECT_EQ(gfx::Rect(), ElectMajorityDamageRect());
+}
+
+TEST_F(AnimatedContentSamplerTest, ElectsLargerOfTwoDamageRects_1) {
+  const gfx::Rect one_rect(0, 0, 1, 1);
+  const gfx::Rect another_rect(0, 0, 2, 2);
+  ObserveDamageRect(one_rect);
+  ObserveDamageRect(another_rect);
+  EXPECT_EQ(another_rect, ElectMajorityDamageRect());
+}
+
+TEST_F(AnimatedContentSamplerTest, ElectsLargerOfTwoDamageRects_2) {
+  const gfx::Rect one_rect(0, 0, 2, 2);
+  const gfx::Rect another_rect(0, 0, 1, 1);
+  ObserveDamageRect(one_rect);
+  ObserveDamageRect(another_rect);
+  EXPECT_EQ(one_rect, ElectMajorityDamageRect());
+}
+
+TEST_F(AnimatedContentSamplerTest, ElectsSameAsMooreDemonstration) {
+  // A more complex sequence (from Moore's web site): Three different Rects with
+  // the same area, but occurring a different number of times.  C should win the
+  // vote.
+  const gfx::Rect rect_a(0, 0, 1, 4);
+  const gfx::Rect rect_b(1, 1, 4, 1);
+  const gfx::Rect rect_c(2, 2, 2, 2);
+  for (int i = 0; i < 3; ++i)
+    ObserveDamageRect(rect_a);
+  for (int i = 0; i < 2; ++i)
+    ObserveDamageRect(rect_c);
+  for (int i = 0; i < 2; ++i)
+    ObserveDamageRect(rect_b);
+  for (int i = 0; i < 3; ++i)
+    ObserveDamageRect(rect_c);
+  ObserveDamageRect(rect_b);
+  for (int i = 0; i < 2; ++i)
+    ObserveDamageRect(rect_c);
+  EXPECT_EQ(rect_c, ElectMajorityDamageRect());
+}
+
+TEST_F(AnimatedContentSamplerTest, Elects24FpsVideoInsteadOf48FpsSpinner) {
+  // Scenario: 24 FPS 720x480 Video versus 48 FPS 96x96 "Busy Spinner"
+  const gfx::Rect video_rect(100, 100, 720, 480);
+  const gfx::Rect spinner_rect(360, 0, 96, 96);
+  for (int i = 0; i < 100; ++i) {
+    // |video_rect| occurs once for every two |spinner_rect|.  Vary the order
+    // of events between the two:
+    ObserveDamageRect(video_rect);
+    ObserveDamageRect(spinner_rect);
+    ObserveDamageRect(spinner_rect);
+    ObserveDamageRect(video_rect);
+    ObserveDamageRect(spinner_rect);
+    ObserveDamageRect(spinner_rect);
+    ObserveDamageRect(spinner_rect);
+    ObserveDamageRect(video_rect);
+    ObserveDamageRect(spinner_rect);
+    ObserveDamageRect(spinner_rect);
+    ObserveDamageRect(video_rect);
+    ObserveDamageRect(spinner_rect);
+  }
+  EXPECT_EQ(video_rect, ElectMajorityDamageRect());
+}
+
+namespace {
+
+// A test scenario for AnimatedContentSamplerParameterizedTest.
+struct Scenario {
+  base::TimeDelta vsync_interval;  // Reflects compositor's update rate.
+  base::TimeDelta min_capture_period;  // Reflects maximum capture rate.
+  base::TimeDelta content_period;  // Reflects content animation rate.
+
+  Scenario(base::TimeDelta v, base::TimeDelta m, base::TimeDelta c)
+      : vsync_interval(v), min_capture_period(m), content_period(c) {
+    CHECK(content_period >= vsync_interval)
+        << "Bad test params: Impossible to animate faster than the compositor.";
+  }
+};
+
+// Value printer for Scenario.
+::std::ostream& operator<<(::std::ostream& os, const Scenario& s) {
+  return os << "{ vsync_interval=" << s.vsync_interval.InMicroseconds()
+            << ", min_capture_period=" << s.min_capture_period.InMicroseconds()
+            << ", content_period=" << s.content_period.InMicroseconds()
+            << " }";
+}
+
+base::TimeDelta FpsAsPeriod(int frame_rate) {
+  return base::TimeDelta::FromSeconds(1) / frame_rate;
+}
+
 }  // namespace
+
+class AnimatedContentSamplerParameterizedTest
+    : public AnimatedContentSamplerTest,
+      public ::testing::WithParamInterface<Scenario> {
+ public:
+  AnimatedContentSamplerParameterizedTest()
+      : count_dropped_frames_(0), count_sampled_frames_(0) {}
+  virtual ~AnimatedContentSamplerParameterizedTest() {}
+
+ protected:
+  typedef std::pair<gfx::Rect, base::TimeTicks> Event;
+
+  virtual base::TimeDelta GetMinCapturePeriod() const OVERRIDE {
+    return GetParam().min_capture_period;
+  }
+
+  // Generate a sequence of events from the compositor pipeline.  The event
+  // times will all be at compositor vsync boundaries.
+  std::vector<Event> GenerateEventSequence(base::TimeTicks begin,
+                                           base::TimeTicks end,
+                                           bool include_content_frame_events,
+                                           bool include_random_events) {
+    DCHECK(GetParam().content_period >= GetParam().vsync_interval);
+    base::TimeTicks next_content_time = begin - GetParam().content_period;
+    std::vector<Event> events;
+    for (base::TimeTicks compositor_time = begin; compositor_time < end;
+         compositor_time += GetParam().vsync_interval) {
+      if (include_content_frame_events && next_content_time < compositor_time) {
+        events.push_back(Event(GetContentDamageRect(), compositor_time));
+        next_content_time += GetParam().content_period;
+      } else if (include_random_events && GetRandomInRange(0, 1) == 0) {
+        events.push_back(Event(GetRandomDamageRect(), compositor_time));
+      }
+    }
+
+    DCHECK(!events.empty());
+    return events;
+  }
+
+  // Feed |events| through the sampler, and detect whether the expected
+  // lock-in/out transition occurs.  Also, track and measure the frame drop
+  // ratio and check it against the expected drop rate.
+  void RunEventSequence(const std::vector<Event> events,
+                        bool was_detecting_before,
+                        bool is_detecting_after,
+                        bool simulate_pipeline_back_pressure) {
+    gfx::Rect first_detected_region;
+
+    EXPECT_EQ(was_detecting_before, sampler()->HasProposal());
+    bool has_detection_switched = false;
+    ResetFrameCounters();
+    for (std::vector<Event>::const_iterator i = events.begin();
+         i != events.end(); ++i) {
+      sampler()->ConsiderPresentationEvent(i->first, i->second);
+
+      // Detect when the sampler locks in/out, and that it stays that way for
+      // all further iterations of this loop.
+      if (!has_detection_switched &&
+          was_detecting_before != sampler()->HasProposal()) {
+        has_detection_switched = true;
+      }
+      ASSERT_EQ(
+          has_detection_switched ? is_detecting_after : was_detecting_before,
+          sampler()->HasProposal());
+
+      if (sampler()->HasProposal()) {
+        // Make sure the sampler doesn't flip-flop and keep proposing sampling
+        // based on locking into different regions.
+        if (first_detected_region.IsEmpty()) {
+          first_detected_region = sampler()->detected_region();
+          ASSERT_FALSE(first_detected_region.IsEmpty());
+        } else {
+          EXPECT_EQ(first_detected_region, sampler()->detected_region());
+        }
+
+        if (simulate_pipeline_back_pressure && GetRandomInRange(0, 2) == 0)
+          ClientCannotSampleFrame(*i);
+        else
+          ClientDoesWhatSamplerProposes(*i);
+      } else {
+        EXPECT_FALSE(sampler()->ShouldSample());
+        if (!simulate_pipeline_back_pressure || GetRandomInRange(0, 2) == 1)
+          sampler()->RecordSample(i->second);
+      }
+    }
+    EXPECT_EQ(is_detecting_after, sampler()->HasProposal());
+    ExpectFrameDropRatioIsCorrect();
+  }
+
+  void ResetFrameCounters() {
+    count_dropped_frames_ = 0;
+    count_sampled_frames_ = 0;
+  }
+
+  // Keep track what the sampler is proposing, and call RecordSample() if it
+  // proposes sampling |event|.
+  void ClientDoesWhatSamplerProposes(const Event& event) {
+    if (sampler()->ShouldSample()) {
+      EXPECT_EQ(GetContentDamageRect(), event.first);
+      sampler()->RecordSample(sampler()->frame_timestamp());
+      ++count_sampled_frames_;
+    } else if (event.first == GetContentDamageRect()) {
+      ++count_dropped_frames_;
+    }
+  }
+
+  // RecordSample() is not called, but for testing, keep track of what the
+  // sampler is proposing for |event|.
+  void ClientCannotSampleFrame(const Event& event) {
+    if (sampler()->ShouldSample()) {
+      EXPECT_EQ(GetContentDamageRect(), event.first);
+      ++count_sampled_frames_;
+    } else if (event.first == GetContentDamageRect()) {
+      ++count_dropped_frames_;
+    }
+  }
+
+  // Confirm the AnimatedContentSampler is not dropping more frames than
+  // expected, given current test parameters.
+  void ExpectFrameDropRatioIsCorrect() {
+    if (count_sampled_frames_ == 0) {
+      EXPECT_EQ(0, count_dropped_frames_);
+      return;
+    }
+    const double content_framerate =
+        1000000.0 / GetParam().content_period.InMicroseconds();
+    const double capture_framerate =
+        1000000.0 / GetParam().min_capture_period.InMicroseconds();
+    const double expected_drop_rate = std::max(
+        0.0, (content_framerate - capture_framerate) / capture_framerate);
+    const double actual_drop_rate =
+        static_cast<double>(count_dropped_frames_) / count_sampled_frames_;
+    EXPECT_NEAR(expected_drop_rate, actual_drop_rate, 0.015);
+  }
+
+ private:
+  // These counters only include the frames with the desired content.
+  int count_dropped_frames_;
+  int count_sampled_frames_;
+};
+
+// Tests that the implementation locks in/out of frames containing stable
+// animated content, whether or not random events are also simultaneously
+// present.
+TEST_P(AnimatedContentSamplerParameterizedTest, DetectsAnimatedContent) {
+  // |begin| refers to the start of an event sequence in terms of the
+  // Compositor's clock.
+  base::TimeTicks begin = InitialTestTimeTicks();
+
+  // Provide random events and expect no lock-in.
+  base::TimeTicks end = begin + base::TimeDelta::FromSeconds(5);
+  RunEventSequence(GenerateEventSequence(begin, end, false, true),
+                   false,
+                   false,
+                   false);
+  begin = end;
+
+  // Provide content frame events with some random events mixed-in, and expect
+  // the sampler to lock-in.
+  end = begin + base::TimeDelta::FromSeconds(5);
+  RunEventSequence(GenerateEventSequence(begin, end, true, true),
+                   false,
+                   true,
+                   false);
+  begin = end;
+
+  // Continue providing content frame events without the random events mixed-in
+  // and expect the lock-in to hold.
+  end = begin + base::TimeDelta::FromSeconds(5);
+  RunEventSequence(GenerateEventSequence(begin, end, true, false),
+                   true,
+                   true,
+                   false);
+  begin = end;
+
+  // Continue providing just content frame events and expect the lock-in to
+  // hold.  Also simulate the capture pipeline experiencing back pressure.
+  end = begin + base::TimeDelta::FromSeconds(20);
+  RunEventSequence(GenerateEventSequence(begin, end, true, false),
+                   true,
+                   true,
+                   true);
+  begin = end;
+
+  // Provide a half-second of random events only, and expect the lock-in to be
+  // broken.
+  end = begin + base::TimeDelta::FromMilliseconds(500);
+  RunEventSequence(GenerateEventSequence(begin, end, false, true),
+                   true,
+                   false,
+                   false);
+  begin = end;
+
+  // Now, go back to providing content frame events, and expect the sampler to
+  // lock-in once again.
+  end = begin + base::TimeDelta::FromSeconds(5);
+  RunEventSequence(GenerateEventSequence(begin, end, true, false),
+                   false,
+                   true,
+                   false);
+  begin = end;
+}
+
+// Tests that AnimatedContentSampler won't lock in to, nor flip-flop between,
+// two animations of the same pixel change rate.  VideoCaptureOracle should
+// revert to using the SmoothEventSampler for these kinds of situations, as
+// there is no "right answer" as to which animation to lock into.
+TEST_P(AnimatedContentSamplerParameterizedTest,
+       DoesNotLockInToTwoCompetingAnimations) {
+  // Don't test when the event stream cannot indicate two separate content
+  // animations under the current test parameters.
+  if (GetParam().content_period < 2 * GetParam().vsync_interval)
+    return;
+
+  // Start the first animation and run for a bit, and expect the sampler to
+  // lock-in.
+  base::TimeTicks begin = InitialTestTimeTicks();
+  base::TimeTicks end = begin + base::TimeDelta::FromSeconds(5);
+  RunEventSequence(GenerateEventSequence(begin, end, true, false),
+                   false,
+                   true,
+                   false);
+  begin = end;
+
+  // Now, keep the first animation and blend in an second animation of the same
+  // size and frame rate, but at a different position.  This will should cause
+  // the sampler to enter an "undetected" state since it's unclear which
+  // animation should be locked into.
+  end = begin + base::TimeDelta::FromSeconds(20);
+  std::vector<Event> first_animation_events =
+      GenerateEventSequence(begin, end, true, false);
+  gfx::Rect second_animation_rect(
+      gfx::Point(0, GetContentDamageRect().height()),
+      GetContentDamageRect().size());
+  std::vector<Event> both_animations_events;
+  base::TimeDelta second_animation_offset = GetParam().vsync_interval;
+  for (std::vector<Event>::const_iterator i = first_animation_events.begin();
+       i != first_animation_events.end(); ++i) {
+    both_animations_events.push_back(*i);
+    both_animations_events.push_back(
+        Event(second_animation_rect, i->second + second_animation_offset));
+  }
+  RunEventSequence(both_animations_events, true, false, false);
+  begin = end;
+
+  // Now, run just the first animation, and expect the sampler to lock-in once
+  // again.
+  end = begin + base::TimeDelta::FromSeconds(5);
+  RunEventSequence(GenerateEventSequence(begin, end, true, false),
+                   false,
+                   true,
+                   false);
+  begin = end;
+
+  // Now, blend in the second animation again, but it has half the frame rate of
+  // the first animation and damage Rects with twice the area.  This will should
+  // cause the sampler to enter an "undetected" state again.  This tests that
+  // pixel-weighting is being accounted for in the sampler's logic.
+  end = begin + base::TimeDelta::FromSeconds(20);
+  first_animation_events = GenerateEventSequence(begin, end, true, false);
+  second_animation_rect.set_width(second_animation_rect.width() * 2);
+  both_animations_events.clear();
+  bool include_second_animation_frame = true;
+  for (std::vector<Event>::const_iterator i = first_animation_events.begin();
+       i != first_animation_events.end(); ++i) {
+    both_animations_events.push_back(*i);
+    if (include_second_animation_frame) {
+      both_animations_events.push_back(
+          Event(second_animation_rect, i->second + second_animation_offset));
+    }
+    include_second_animation_frame = !include_second_animation_frame;
+  }
+  RunEventSequence(both_animations_events, true, false, false);
+  begin = end;
+}
+
+// Tests that the frame timestamps are smooth; meaning, that when run through a
+// simulated compositor, each frame is held displayed for the right number of
+// v-sync intervals.
+TEST_P(AnimatedContentSamplerParameterizedTest, FrameTimestampsAreSmooth) {
+  // Generate 30 seconds of animated content events, run the events through
+  // AnimatedContentSampler, and record all frame timestamps being proposed
+  // once lock-in is continuous.
+  base::TimeTicks begin = InitialTestTimeTicks();
+  std::vector<Event> events = GenerateEventSequence(
+      begin,
+      begin + base::TimeDelta::FromSeconds(20),
+      true,
+      false);
+  typedef std::vector<base::TimeTicks> Timestamps;
+  Timestamps frame_timestamps;
+  for (std::vector<Event>::const_iterator i = events.begin(); i != events.end();
+       ++i) {
+    sampler()->ConsiderPresentationEvent(i->first, i->second);
+    if (sampler()->HasProposal()) {
+      if (sampler()->ShouldSample()) {
+        frame_timestamps.push_back(sampler()->frame_timestamp());
+        sampler()->RecordSample(sampler()->frame_timestamp());
+      }
+    } else {
+      frame_timestamps.clear();  // Reset until continuous lock-in.
+    }
+  }
+  ASSERT_LE(2u, frame_timestamps.size());
+
+  // Iterate through the |frame_timestamps|, building a histogram counting the
+  // number of times each frame was displayed k times.  For example, 10 frames
+  // of 30 Hz content on a 60 Hz v-sync interval should result in
+  // display_counts[2] == 10.  Quit early if any one frame was obviously
+  // repeated too many times.
+  const int64 max_expected_repeats_per_frame = 1 +
+      std::max(GetParam().min_capture_period, GetParam().content_period) /
+          GetParam().vsync_interval;
+  std::vector<size_t> display_counts(max_expected_repeats_per_frame + 1, 0);
+  base::TimeTicks last_present_time = frame_timestamps.front();
+  for (Timestamps::const_iterator i = frame_timestamps.begin() + 1;
+       i != frame_timestamps.end(); ++i) {
+    const size_t num_vsync_intervals = static_cast<size_t>(
+        (*i - last_present_time) / GetParam().vsync_interval);
+    ASSERT_LT(0u, num_vsync_intervals);
+    ASSERT_GT(display_counts.size(), num_vsync_intervals);  // Quit early.
+    ++display_counts[num_vsync_intervals];
+    last_present_time += num_vsync_intervals * GetParam().vsync_interval;
+  }
+
+  // Analyze the histogram for an expected result pattern.  If the frame
+  // timestamps are smooth, there should only be one or two buckets with
+  // non-zero counts and they should be next to each other.  Because the clock
+  // precision for the event_times provided to the sampler is very granular
+  // (i.e., the vsync_interval), it's okay if other buckets have a tiny "stray"
+  // count in this test.
+  size_t highest_count = 0;
+  size_t second_highest_count = 0;
+  for (size_t repeats = 1; repeats < display_counts.size(); ++repeats) {
+    DVLOG(1) << "display_counts[" << repeats << "] is "
+             << display_counts[repeats];
+    if (display_counts[repeats] >= highest_count) {
+      second_highest_count = highest_count;
+      highest_count = display_counts[repeats];
+    } else if (display_counts[repeats] > second_highest_count) {
+      second_highest_count = display_counts[repeats];
+    }
+  }
+  size_t stray_count_remaining =
+      (frame_timestamps.size() - 1) - (highest_count + second_highest_count);
+  // Expect no more than 0.75% of frames fall outside the two main buckets.
+  EXPECT_GT(frame_timestamps.size() * 75 / 10000, stray_count_remaining);
+  for (size_t repeats = 1; repeats < display_counts.size() - 1; ++repeats) {
+    if (display_counts[repeats] == highest_count) {
+      EXPECT_EQ(second_highest_count, display_counts[repeats + 1]);
+      ++repeats;
+    } else if (display_counts[repeats] == second_highest_count) {
+      EXPECT_EQ(highest_count, display_counts[repeats + 1]);
+      ++repeats;
+    } else {
+      EXPECT_GE(stray_count_remaining, display_counts[repeats]);
+      stray_count_remaining -= display_counts[repeats];
+    }
+  }
+}
+
+// Tests that frame timestamps are "lightly pushed" back towards the original
+// presentation event times, which tells us the AnimatedContentSampler can
+// account for sources of timestamp drift and correct the drift.
+TEST_P(AnimatedContentSamplerParameterizedTest,
+       FrameTimestampsConvergeTowardsEventTimes) {
+  const int max_drift_increment_millis = 3;
+
+  // Generate a full minute of events.
+  const base::TimeTicks begin = InitialTestTimeTicks();
+  const base::TimeTicks end = begin + base::TimeDelta::FromMinutes(1);
+  std::vector<Event> events = GenerateEventSequence(begin, end, true, false);
+
+  // Modify the event sequence so that 1-3 ms of additional drift is suddenly
+  // present every 100 events.  This is meant to simulate that, external to
+  // AnimatedContentSampler, the video hardware vsync timebase is being
+  // refreshed and is showing severe drift from the system clock.
+  base::TimeDelta accumulated_drift;
+  for (size_t i = 1; i < events.size(); ++i) {
+    if (i % 100 == 0) {
+      accumulated_drift += base::TimeDelta::FromMilliseconds(
+          GetRandomInRange(1, max_drift_increment_millis + 1));
+    }
+    events[i].second += accumulated_drift;
+  }
+
+  // Run all the events through the sampler and track the last rewritten frame
+  // timestamp.
+  base::TimeTicks last_frame_timestamp;
+  for (std::vector<Event>::const_iterator i = events.begin(); i != events.end();
+       ++i) {
+    sampler()->ConsiderPresentationEvent(i->first, i->second);
+    if (sampler()->ShouldSample())
+      last_frame_timestamp = sampler()->frame_timestamp();
+  }
+
+  // If drift was accounted for, the |last_frame_timestamp| should be close to
+  // the last event's timestamp.
+  const base::TimeDelta total_error =
+      events.back().second - last_frame_timestamp;
+  const base::TimeDelta max_acceptable_error = GetParam().min_capture_period +
+      base::TimeDelta::FromMilliseconds(max_drift_increment_millis);
+  EXPECT_NEAR(0.0,
+              total_error.InMicroseconds(),
+              max_acceptable_error.InMicroseconds());
+}
+
+INSTANTIATE_TEST_CASE_P(
+    ,
+    AnimatedContentSamplerParameterizedTest,
+    ::testing::Values(
+         // Typical frame rate content: Compositor runs at 60 Hz, capture at 30
+         // Hz, and content video animates at 30, 25, or 24 Hz.
+         Scenario(FpsAsPeriod(60), FpsAsPeriod(30), FpsAsPeriod(30)),
+         Scenario(FpsAsPeriod(60), FpsAsPeriod(30), FpsAsPeriod(25)),
+         Scenario(FpsAsPeriod(60), FpsAsPeriod(30), FpsAsPeriod(24)),
+
+         // High frame rate content that leverages the Compositor's
+         // capabilities, but capture is still at 30 Hz.
+         Scenario(FpsAsPeriod(60), FpsAsPeriod(30), FpsAsPeriod(60)),
+         Scenario(FpsAsPeriod(60), FpsAsPeriod(30), FpsAsPeriod(50)),
+         Scenario(FpsAsPeriod(60), FpsAsPeriod(30), FpsAsPeriod(48)),
+
+         // High frame rate content that leverages the Compositor's
+         // capabilities, and capture is also a buttery 60 Hz.
+         Scenario(FpsAsPeriod(60), FpsAsPeriod(60), FpsAsPeriod(60)),
+         Scenario(FpsAsPeriod(60), FpsAsPeriod(60), FpsAsPeriod(50)),
+         Scenario(FpsAsPeriod(60), FpsAsPeriod(60), FpsAsPeriod(48)),
+
+         // On some platforms, the Compositor runs at 50 Hz.
+         Scenario(FpsAsPeriod(50), FpsAsPeriod(30), FpsAsPeriod(30)),
+         Scenario(FpsAsPeriod(50), FpsAsPeriod(30), FpsAsPeriod(25)),
+         Scenario(FpsAsPeriod(50), FpsAsPeriod(30), FpsAsPeriod(24)),
+         Scenario(FpsAsPeriod(50), FpsAsPeriod(30), FpsAsPeriod(50)),
+         Scenario(FpsAsPeriod(50), FpsAsPeriod(30), FpsAsPeriod(48)),
+
+         // Stable, but non-standard content frame rates.
+         Scenario(FpsAsPeriod(60), FpsAsPeriod(30), FpsAsPeriod(16)),
+         Scenario(FpsAsPeriod(60), FpsAsPeriod(30), FpsAsPeriod(20)),
+         Scenario(FpsAsPeriod(60), FpsAsPeriod(30), FpsAsPeriod(23)),
+         Scenario(FpsAsPeriod(60), FpsAsPeriod(30), FpsAsPeriod(26)),
+         Scenario(FpsAsPeriod(60), FpsAsPeriod(30), FpsAsPeriod(27)),
+         Scenario(FpsAsPeriod(60), FpsAsPeriod(30), FpsAsPeriod(28)),
+         Scenario(FpsAsPeriod(60), FpsAsPeriod(30), FpsAsPeriod(29)),
+         Scenario(FpsAsPeriod(60), FpsAsPeriod(30), FpsAsPeriod(31)),
+         Scenario(FpsAsPeriod(60), FpsAsPeriod(30), FpsAsPeriod(32)),
+         Scenario(FpsAsPeriod(60), FpsAsPeriod(30), FpsAsPeriod(33))));
+
+// Tests that VideoCaptureOracle filters out events whose timestamps are
+// decreasing.
+TEST(VideoCaptureOracleTest, EnforcesEventTimeMonotonicity) {
+  const base::TimeDelta min_capture_period =
+      base::TimeDelta::FromSeconds(1) / 30;
+  const gfx::Rect damage_rect(0, 0, 1280, 720);
+  const base::TimeDelta event_increment = min_capture_period * 2;
+
+  VideoCaptureOracle oracle(min_capture_period, true);
+
+  base::TimeTicks t = InitialTestTimeTicks();
+  for (int i = 0; i < 10; ++i) {
+    t += event_increment;
+    ASSERT_TRUE(oracle.ObserveEventAndDecideCapture(
+        VideoCaptureOracle::kCompositorUpdate,
+        damage_rect, t));
+  }
+
+  base::TimeTicks furthest_event_time = t;
+  for (int i = 0; i < 10; ++i) {
+    t -= event_increment;
+    ASSERT_FALSE(oracle.ObserveEventAndDecideCapture(
+        VideoCaptureOracle::kCompositorUpdate,
+        damage_rect, t));
+  }
+
+  t = furthest_event_time;
+  for (int i = 0; i < 10; ++i) {
+    t += event_increment;
+    ASSERT_TRUE(oracle.ObserveEventAndDecideCapture(
+        VideoCaptureOracle::kCompositorUpdate,
+        damage_rect, t));
+  }
+}
+
+// Tests that VideoCaptureOracle is enforcing the requirement that captured
+// frames are delivered in order.  Otherwise, downstream consumers could be
+// tripped-up by out-of-order frames or frame timestamps.
+TEST(VideoCaptureOracleTest, EnforcesFramesDeliveredInOrder) {
+  const base::TimeDelta min_capture_period =
+      base::TimeDelta::FromSeconds(1) / 30;
+  const gfx::Rect damage_rect(0, 0, 1280, 720);
+  const base::TimeDelta event_increment = min_capture_period * 2;
+
+  VideoCaptureOracle oracle(min_capture_period, true);
+
+  // Most basic scenario: Frames delivered one at a time, with no additional
+  // captures in-between deliveries.
+  base::TimeTicks t = InitialTestTimeTicks();
+  int last_frame_number;
+  base::TimeTicks ignored;
+  for (int i = 0; i < 10; ++i) {
+    t += event_increment;
+    ASSERT_TRUE(oracle.ObserveEventAndDecideCapture(
+        VideoCaptureOracle::kCompositorUpdate,
+        damage_rect, t));
+    last_frame_number = oracle.RecordCapture();
+    ASSERT_TRUE(oracle.CompleteCapture(last_frame_number, &ignored));
+  }
+
+  // Basic pipelined scenario: More than one frame in-flight at delivery points.
+  for (int i = 0; i < 50; ++i) {
+    const int num_in_flight = 1 + i % 3;
+    for (int j = 0; j < num_in_flight; ++j) {
+      t += event_increment;
+      ASSERT_TRUE(oracle.ObserveEventAndDecideCapture(
+          VideoCaptureOracle::kCompositorUpdate,
+          damage_rect, t));
+      last_frame_number = oracle.RecordCapture();
+    }
+    for (int j = num_in_flight - 1; j >= 0; --j) {
+      ASSERT_TRUE(oracle.CompleteCapture(last_frame_number - j, &ignored));
+    }
+  }
+
+  // Pipelined scenario with out-of-order delivery attempts rejected.
+  for (int i = 0; i < 50; ++i) {
+    const int num_in_flight = 1 + i % 3;
+    for (int j = 0; j < num_in_flight; ++j) {
+      t += event_increment;
+      ASSERT_TRUE(oracle.ObserveEventAndDecideCapture(
+          VideoCaptureOracle::kCompositorUpdate,
+          damage_rect, t));
+      last_frame_number = oracle.RecordCapture();
+    }
+    ASSERT_TRUE(oracle.CompleteCapture(last_frame_number, &ignored));
+    for (int j = 1; j < num_in_flight; ++j) {
+      ASSERT_FALSE(oracle.CompleteCapture(last_frame_number - j, &ignored));
+    }
+  }
+}
+
+// Tests that VideoCaptureOracle transitions between using its two samplers in a
+// way that does not introduce severe jank, pauses, etc.
+TEST(VideoCaptureOracleTest, TransitionsSmoothlyBetweenSamplers) {
+  const base::TimeDelta min_capture_period =
+      base::TimeDelta::FromSeconds(1) / 30;
+  const gfx::Rect animation_damage_rect(0, 0, 1280, 720);
+  const base::TimeDelta event_increment = min_capture_period * 2;
+
+  VideoCaptureOracle oracle(min_capture_period, true);
+
+  // Run sequences of animation events and non-animation events through the
+  // oracle.  As the oracle transitions between each sampler, make sure the
+  // frame timestamps won't trip-up downstream consumers.
+  base::TimeTicks t = InitialTestTimeTicks();
+  base::TimeTicks last_frame_timestamp;
+  for (int i = 0; i < 1000; ++i) {
+    t += event_increment;
+
+    // For every 100 events, provide 50 that will cause the
+    // AnimatedContentSampler to lock-in, followed by 50 that will cause it to
+    // lock-out (i.e., the oracle will use the SmoothEventSampler instead).
+    const bool provide_animated_content_event =
+        (i % 100) >= 25 && (i % 100) < 75;
+
+    // Only the few events that trigger the lock-out transition should be
+    // dropped, because the AnimatedContentSampler doesn't yet realize the
+    // animation ended.  Otherwise, the oracle should always decide to sample
+    // because one of its samplers says to.
+    const bool require_oracle_says_sample = (i % 100) < 75 || (i % 100) >= 78;
+    const bool oracle_says_sample = oracle.ObserveEventAndDecideCapture(
+        VideoCaptureOracle::kCompositorUpdate,
+        provide_animated_content_event ? animation_damage_rect : gfx::Rect(),
+        t);
+    if (require_oracle_says_sample)
+      ASSERT_TRUE(oracle_says_sample);
+    if (!oracle_says_sample)
+      continue;
+
+    const int frame_number = oracle.RecordCapture();
+
+    base::TimeTicks frame_timestamp;
+    ASSERT_TRUE(oracle.CompleteCapture(frame_number, &frame_timestamp));
+    ASSERT_FALSE(frame_timestamp.is_null());
+    if (!last_frame_timestamp.is_null()) {
+      const base::TimeDelta delta = frame_timestamp - last_frame_timestamp;
+      EXPECT_LE(event_increment.InMicroseconds(), delta.InMicroseconds());
+      // Right after the AnimatedContentSampler lock-out transition, there were
+      // a few frames dropped, so allow a gap in the timestamps.  Otherwise, the
+      // delta between frame timestamps should never be more than 2X the
+      // |event_increment|.
+      const base::TimeDelta max_acceptable_delta = (i % 100) == 78 ?
+          event_increment * 5 : event_increment * 2;
+      EXPECT_GE(max_acceptable_delta.InMicroseconds(), delta.InMicroseconds());
+    }
+    last_frame_timestamp = frame_timestamp;
+  }
+}
+
 }  // namespace content