Use input events to improve vsync scheduling

cc/vsync_time_source_unittest.cc

Index: cc/vsync_time_source_unittest.cc
diff --git a/cc/vsync_time_source_unittest.cc b/cc/vsync_time_source_unittest.cc
index 9833614e7a13c9241675e8719b301f47645bc8a2..f3af85f75742e901f9a812f6e183af6431c893c3 100644
--- a/cc/vsync_time_source_unittest.cc
+++ b/cc/vsync_time_source_unittest.cc
@@ -31,17 +31,34 @@ class FakeVSyncProvider : public VSyncProvider {
   VSyncClient* client_;
 };
 
+class FakeVSyncTimeSource : public cc::VSyncTimeSource {
+ public:
+  static scoped_refptr<FakeVSyncTimeSource> create(VSyncProvider* provider) {
+      return make_scoped_refptr(new FakeVSyncTimeSource(provider));
+  }
+
+  void SetNow(base::TimeTicks time) { now_ = time; }
+  virtual base::TimeTicks Now() const OVERRIDE { return now_; }
+
+ protected:
+  explicit FakeVSyncTimeSource(VSyncProvider* provider)
+    : VSyncTimeSource(provider) {}
+  virtual ~FakeVSyncTimeSource() {}
+
+  base::TimeTicks now_;
+};
+
 class VSyncTimeSourceTest : public testing::Test {
  public:
   VSyncTimeSourceTest()
-      : timer_(VSyncTimeSource::create(&provider_)) {
+      : timer_(FakeVSyncTimeSource::create(&provider_)) {
     timer_->setClient(&client_);
   }
 
  protected:
   FakeTimeSourceClient client_;
   FakeVSyncProvider provider_;
-  scoped_refptr<VSyncTimeSource> timer_;
+  scoped_refptr<FakeVSyncTimeSource> timer_;
 };
 
 TEST_F(VSyncTimeSourceTest, TaskPostedAndTickCalled)
@@ -99,5 +116,47 @@ TEST_F(VSyncTimeSourceTest, ValidNextTickTime)
   ASSERT_EQ(timer_->nextTickTime(), frame_time + interval);
 }
 
+TEST_F(VSyncTimeSourceTest, SynthesizeVSyncFromInput)
+{
+  base::TimeTicks current_time;
+  base::TimeDelta interval = base::TimeDelta::FromSeconds(1);
+
+  // Establish a time base and interval.
+  timer_->setTimebaseAndInterval(current_time, interval);
+
+  // An input event when the timer is inactive should do nothing.
+  timer_->DidReceiveLastInputEventForVSync();
+  EXPECT_FALSE(client_.tickCalled());
+  ASSERT_EQ(timer_->lastTickTime(), base::TimeTicks());
+
+  // An input event should synthesize a vsync event with a frame time estimated
+  // from the current time.
+  current_time += interval;
+  timer_->SetNow(current_time);
+  timer_->setActive(true);
+  timer_->DidReceiveLastInputEventForVSync();
+  EXPECT_TRUE(client_.tickCalled());
+  ASSERT_EQ(timer_->lastTickTime(), current_time);
+  client_.reset();
+
+  // A vsync notification immediately following the input should be ignored.
+  provider_.Trigger(current_time);
+  EXPECT_FALSE(client_.tickCalled());
+
+  // A vsync notification for the next frame should not be ignored.
+  current_time += interval;
+  provider_.Trigger(current_time);
+  EXPECT_TRUE(client_.tickCalled());
+  ASSERT_EQ(timer_->lastTickTime(), current_time);
+  client_.reset();
+
+  // The next input event should also trigger a tick, because it signifies a
+  // start of a new frame.
+  current_time += interval;
+  provider_.Trigger(current_time);
+  EXPECT_TRUE(client_.tickCalled());
+  ASSERT_EQ(timer_->lastTickTime(), current_time);
+}
+
 }  // namespace
 }  // namespace cc