Input latency performance test that uses tracing.

chrome/test/perf/rendering/latency_tests.cc

Index: chrome/test/perf/rendering/latency_tests.cc
diff --git a/chrome/test/perf/rendering/latency_tests.cc b/chrome/test/perf/rendering/latency_tests.cc
new file mode 100644
index 0000000000000000000000000000000000000000..a98b86fe8330ca34b6e8c91ee4f4030994786489
--- /dev/null
+++ b/chrome/test/perf/rendering/latency_tests.cc
@@ -0,0 +1,539 @@
+// Copyright (c) 2011 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 "base/command_line.h"
+#include "base/file_util.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/path_service.h"
+#include "base/string_number_conversions.h"
+#include "base/stringprintf.h"
+#include "base/test/test_switches.h"
+#include "base/test/trace_event_analyzer.h"
+#include "base/threading/platform_thread.h"
+#include "base/timer.h"
+#include "base/version.h"
+#include "chrome/browser/ui/browser.h"
+#include "chrome/browser/ui/tab_contents/tab_contents_wrapper.h"
+#include "chrome/common/chrome_paths.h"
+#include "chrome/common/chrome_switches.h"
+#include "chrome/test/base/tracing.h"
+#include "chrome/test/base/ui_test_utils.h"
+#include "chrome/test/perf/browser_perf_test.h"
+#include "chrome/test/perf/perf_test.h"
+#include "content/browser/renderer_host/render_view_host.h"
+#include "content/browser/tab_contents/tab_contents.h"
+#include "content/public/common/content_switches.h"
+#include "third_party/WebKit/Source/WebKit/chromium/public/WebInputEvent.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+// Run with --vmodule=latency_tests=1 to print verbose latency info.
+
+// How is latency measured?
+//
+// The test injects mouse moves many times per frame from the browser via
+// RenderWidgetHost. Each input has a unique x coordinate. When the javascript
+// handler receives the input, it stores the coordinate for later use in the
+// requestAnimationFrame callback. In RAF, the test paints using the x
+// coordinate as a color (in software, it sets the color of a table; in webgl,
+// it executes a glClearColor). Trace events emit the color when it is picked up
+// by either UpdateRect for software or gles2_cmd_decoder/glClear for webgl.
+//
+// Each UpdateRect (software) or SwapBuffers (webgl) is considered to be a frame
+// boundary that will be used to measure latency in number of frames. Starting
+// from a frame boundary Y, the test first determines what mouse x coordinate
+// was represented by the color at that frame boundary. Then, the test walks
+// backward through the trace events to find the input event matching that
+// x coordinate. Then, the test find the nearest frame boundary X to the input
+// event (may be before or after). The number of frame boundaries is then
+// counted between X and Y to determine the input latency.
+//
+// By injecting mouse moves many times per frame, we reduce flakiness in the
+// finding of the nearest frame boundary.
+//
+// This test only measures the latency introduced by chrome code -- it does not
+// measure latency introduced by mouse drivers or the GL driver or the OS window
+// manager. The actual latency seen by a user is more than what is reported by
+// this test.
+//
+// Current modes:
+// - Software RAF
+// - WebGL RAF
+
+namespace {
+
+using namespace trace_analyzer;
+
+enum LatencyTestFlags {
+  kInputHeavy   = 1 << 0,
+  kInputDirty   = 1 << 1,
+  kRafHeavy     = 1 << 2,
+  kPaintHeavy   = 1 << 3
+};
+
+int kWebGLCanvasWidth = 10;

[nduca, 2011/12/21 20:24:23]

should these be const? you've got them named as if they're const.

[jbates, 2011/12/22 02:41:17]

Done.

+int kNumFrames = 60;
+int kInputsPerFrame = 16;
+// Magic number to identify certain glClear events.
+int kClearColorGreen = 137;
+int kMouseY = 5;
+
+class LatencyTest : public BrowserPerfTest {
+ public:
+  LatencyTest() :
+      query_instant_(Query(EVENT_PHASE) ==
+                     Query::Phase(TRACE_EVENT_PHASE_INSTANT)),

[nduca, 2011/12/21 20:24:23]

you might make a note that these will be initialized in runtests... or change
where they init, or something... its a bit confusing that they're all false up
front.

[jbates, 2011/12/22 02:41:17]

Done. (Sadly no default constructor on Query)

+      query_swaps_(Query::Bool(false)),
+      query_inputs_(Query::Bool(false)),
+      query_blits_(Query::Bool(false)),
+      query_clears_(Query::Bool(false)),
+      mouse_x_(0),
+      tab_width_(0),
+      delay_time_ms_(0),
+      num_frames_(0),
+      verbose_(false),
+      test_flags_(0) {}
+
+  virtual void SetUpCommandLine(CommandLine* command_line) {

[Paweł Hajdan Jr., 2011/12/21 09:50:29]

nit: OVERRIDE

[jbates, 2011/12/21 19:34:18]

Done.

+    BrowserPerfTest::SetUpCommandLine(command_line);
+    // This enables DOM automation for tab contents.
+    EnableDOMAutomation();
+#ifdef TEST_THREADED_COMPOSITING_LATENCY

[Paweł Hajdan Jr., 2011/12/21 09:50:29]

Why is this pre-processor controlled? I don't see
TEST_THREADED_COMPOSITING_LATENCY in any other place. Why not just pass the
command-line flag?

[jbates, 2011/12/21 19:34:18]

Done.

+    command_line->AppendSwitch(switches::kEnableThreadedCompositing);
+#endif
+    // Default behavior is to thumbnail the tab after 0.5 seconds, causing
+    // a nasty frame hitch and disturbing the latency test. Fix that:
+    command_line->AppendSwitch(switches::kEnableInBrowserThumbnailing);
+    command_line->AppendSwitch(switches::kDisableBackgroundNetworking);
+  }
+
+  // Run test with specified |mode| and |behaviors|.
+  // |mode| can be webgl or software.
+  // |behaviors| is a list of combinations of LatencyTestFlags.
+  void RunTest(const std::string& mode, const std::vector<int>& behaviors);
+
+  std::vector<int> GetAllBehaviors() {
+    std::vector<int> behaviors;
+    int max_behaviors = kInputHeavy | kInputDirty | kRafHeavy | kPaintHeavy;
+    for (int i = 0; i <= max_behaviors; ++i)
+      behaviors.push_back(i);
+    return behaviors;
+  }
+
+private:

[Paweł Hajdan Jr., 2011/12/21 09:50:29]

nit: Indent +1.

[jbates, 2011/12/21 19:34:18]

Done.

+  void RunTestInternal(const std::string& test_url,
+                       bool send_inputs,
+                       int input_delay_ms);
+
+  double CalculateLatency();
+
+  std::string GetTraceName(int flags) {
+    if (flags == 0)
+      return "simple";
+    std::string name;
+    if (flags & kInputHeavy)
+      name += "ih";
+    if (flags & kInputDirty)
+      name += std::string(name.empty()? "" : "_") + "id";
+    if (flags & kRafHeavy)
+      name += std::string(name.empty()? "" : "_") + "rh";
+    if (flags & kPaintHeavy)
+      name += std::string(name.empty()? "" : "_") + "ph";
+    return name;
+  }
+
+  std::string GetUrlModeString(int flags) {
+    std::string mode = "&mode=" + mode_;
+    if (flags & kInputHeavy)
+      mode += "&inputHeavy=true";
+    if (flags & kInputDirty)
+      mode += "&inputDirty=true";
+    if (flags & kRafHeavy)
+      mode += "&rafHeavy=true";
+    if (flags & kPaintHeavy)
+      mode += "&paintHeavy=true";
+    return mode;
+  }
+
+  std::string GetUrl(int flags) {
+    std::string test_url =
+        net::FilePathToFileURL(test_path_).possibly_invalid_spec();
+    test_url += "?numFrames=" + base::IntToString(num_frames_);
+    test_url += "&canvasWidth=" + base::IntToString(kWebGLCanvasWidth);
+    test_url += "&clearColorGreen=" + base::IntToString(kClearColorGreen);
+    test_url += "&delayTimeMS=" + base::IntToString(delay_time_ms_);
+    test_url += "&y=" + base::IntToString(kMouseY);
+    return test_url + GetUrlModeString(flags);
+  }
+
+  int GetMeanFrameTime() const {
+    TraceEventVector events;
+    // Search for compositor swaps (or UpdateRects in the software path).
+    analyzer_->FindEvents(query_swaps_, &events);
+    RateStats stats;
+    bool success = GetRateStats(events, &stats);
+    EXPECT_TRUE(success);
+    if (!success)
+      return 16000;

[nduca, 2011/12/21 20:24:23]

Comment to explain why this magic number is used?

[jbates, 2011/12/22 02:41:17]

Done.

+
+    // Check that the number of swaps is close to kNumFrames.
+    EXPECT_LT(num_frames_ - num_frames_/4, static_cast<int>(events.size()));

[Paweł Hajdan Jr., 2011/12/21 09:50:29]

nit: Spaces around "/".

[jbates, 2011/12/21 19:34:18]

Done.

+    return static_cast<int>(stats.mean_us);
+  }
+
+  void SendInput() {
+    RenderViewHost* rvh = browser()->GetSelectedTabContentsWrapper()->
+        tab_contents()->render_view_host();
+    WebKit::WebMouseEvent mouse_event;
+    mouse_event.movementX = 1;
+    mouse_x_ += mouse_event.movementX;
+    // Wrap mouse_x_ when it's near the edge of the tab.
+    if (mouse_x_ > tab_width_ - 5)
+      mouse_x_ = 1;
+    mouse_event.x = mouse_event.windowX = mouse_x_;
+    // Set y coordinate to be a few pixels down from the top of the window,
+    // so that it is between the top and bottom of the canvas.
+    mouse_event.y = mouse_event.windowY = 5;
+    mouse_event.type = WebKit::WebInputEvent::MouseMove;
+    TRACE_EVENT_INSTANT1("test_latency", "MouseEventBegin", "x", mouse_x_);
+    rvh->ForwardMouseEvent(mouse_event);

[nduca, 2011/12/21 20:24:23]

/me wonders out loud whether this will cleanly extend to touch?

[jbates, 2011/12/22 02:41:17]

Yeah, it seems like it would be a trivial update to test the "mouse move"
equivalent of touch inputs.

+  }
+
+  void PrintEvents(const TraceEventVector& events) {
+    bool is_software = (mode_ == "software");
+    // Print trace data.

[nduca, 2011/12/21 20:24:23]

comment doesn't add a lot of value methinks

[jbates, 2011/12/22 02:41:17]

Done.

+    int swap_count = 0;
+    for (size_t i = 0; i < events.size(); ++i) {
+      if (events[i]->name == "MouseEventBegin") {
+        printf("%03d ", events[i]->GetKnownArgAsInt("x"));
+      }
+      else if (events[i]->name == "DoClear") {

[Paweł Hajdan Jr., 2011/12/21 09:50:29]

nit: move this to the previous line, same below, i.e.:

if (...) {
} else if (...) {
} else {
}

[jbates, 2011/12/21 19:34:18]

Done.

+        printf("Clr%03d ", events[i]->GetKnownArgAsInt("red"));
+      }
+      else if (events[i]->name == "DoBlit") {
+        // WebGL context swap buffers.
+        printf("BLT ");
+      }
+      else if (events[i]->name == "SwapBuffers") {
+        // Compositor context swap buffers.
+        ++swap_count;
+        printf("|\nframe %03d: ", swap_count + 1);
+      }
+      else if (is_software && events[i]->name == "UpdateRect") {
+        ++swap_count;
+        printf("(%d)|\nframe %03d: ",
+                events[i]->GetKnownArgAsInt("color"), swap_count + 1);
+      }
+    }
+    printf("\n");
+  }
+
+  FilePath test_path_;

[Paweł Hajdan Jr., 2011/12/21 09:50:29]

nit: Please comment member variables.

[jbates, 2011/12/21 19:34:18]

Done.

+  Query query_instant_;
+  Query query_swaps_;
+  Query query_inputs_;
+  Query query_blits_;
+  Query query_clears_;
+  scoped_ptr<TraceAnalyzer> analyzer_;
+  int mouse_x_;
+  int tab_width_;
+  base::RepeatingTimer<LatencyTest> timer_;
+  std::string mode_;
+  int delay_time_ms_;
+  int num_frames_;
+  std::map<int, double> latencies_;
+  bool verbose_;
+  int test_flags_;
+};
+
+void LatencyTest::RunTest(const std::string& mode,

[nduca, 2011/12/21 20:24:23]

odd that you're using a mode string but an enum for test flags. I'd have
expected a mode enum...

[jbates, 2011/12/22 02:41:17]

Done.

+                          const std::vector<int>& behaviors) {

[nduca, 2011/12/21 20:24:23]

Also, a bit confused that some functions are implemented in the class definition
and some outside. If that's standard, no need to explain, I've not had much
occasion to have a class local to a file before.  :)

[jbates, 2011/12/22 02:41:17]

Moved them out (to make the changes easier to follow I did the move as a
separate cl upload from the other changes).

+  mode_ = mode;
+  verbose_ = (logging::GetVlogLevel("latency_tests") > 0);
+
+  // Construct queries for searching trace events via TraceAnalyzer.
+  int initial_flags = 0;
+  if (mode_ == "webgl") {
+    query_swaps_ = query_instant_ &&
+        Query(EVENT_NAME) == Query::String("SwapBuffers") &&
+        Query(EVENT_ARG, "width") != Query::Int(kWebGLCanvasWidth);
+  } else if (mode_ == "software") {
+    // Run software with kPaintHeavy the first time when no inputs are
+    // triggering paints -- otherwise it won't update each frame.

[nduca, 2011/12/21 20:24:23]

Not sure I follow this. Also, this feels out of place in a block of code that
says its setting up queries.

[jbates, 2011/12/22 02:41:17]

Done.

+    initial_flags = static_cast<int>(kPaintHeavy);
+    // Software updates need to have x=0 and y=0 to contain the input color.
+    query_swaps_ = query_instant_ &&
+        Query(EVENT_NAME) == Query::String("UpdateRect") &&
+        Query(EVENT_ARG, "x+y") == Query::Int(0);
+  }
+  query_inputs_ = query_instant_ &&
+      Query(EVENT_NAME) == Query::String("MouseEventBegin");
+  query_blits_ = query_instant_ &&
+      Query(EVENT_NAME) == Query::String("DoBlit") &&
+      Query(EVENT_ARG, "width") == Query::Int(kWebGLCanvasWidth);
+  query_clears_ = query_instant_ &&
+      Query(EVENT_NAME) == Query::String("DoClear") &&
+      Query(EVENT_ARG, "green") == Query::Int(kClearColorGreen);
+  Query query_width_swaps = query_swaps_;
+  if (mode_ == "software") {
+    query_width_swaps = query_instant_ &&
+        Query(EVENT_NAME) == Query::String("UpdateRectWidth") &&
+        Query(EVENT_ARG, "width") > Query::Int(kWebGLCanvasWidth);
+  }
+
+  // Set path to test html.
+  PathService::Get(chrome::DIR_TEST_DATA, &test_path_);

[Paweł Hajdan Jr., 2011/12/21 09:50:29]

Check the return value.

[jbates, 2011/12/21 19:34:18]

Done.

+  test_path_ = test_path_.Append(FILE_PATH_LITERAL("perf"));
+  test_path_ = test_path_.Append(FILE_PATH_LITERAL("latency_suite.html"));
+  ASSERT_TRUE(file_util::PathExists(test_path_))
+      << "Missing test file: " << test_path_.value();
+
+  // Run once with defaults to measure the frame times.
+  delay_time_ms_ = 0;
+  // kNumFrames may be very high, but we only need a few frames to measure
+  // average frame times.
+  num_frames_ = 30;
+  RunTestInternal(GetUrl(initial_flags), false, 0);
+
+  // Get width of tab so that we know the limit of x coordinates for the
+  // injected mouse inputs.
+  const TraceEvent* swap_event = analyzer_->FindOneEvent(query_width_swaps);
+  ASSERT_TRUE(swap_event);
+  tab_width_ = swap_event->GetKnownArgAsInt("width");
+  // Keep printf output clean by limiting input coords to three digits:
+  tab_width_ = (tab_width_ < 1000) ? tab_width_ : 999;
+  // Sanity check the tab_width -- it should be more than 100 pixels.
+  EXPECT_GT(tab_width_, 100);
+
+  int mean_frame_time_us = GetMeanFrameTime();

[nduca, 2011/12/21 20:24:23]

why are we mixing micros and ms?

[jbates, 2011/12/22 02:41:17]

Done.

+  if (verbose_)
+    printf("Mean frame time micros = %d\n", mean_frame_time_us);
+  // Delay time is 2x the average frame time.
+  delay_time_ms_ = 2 * mean_frame_time_us / 1000;
+  // Calculate delay time between inputs based on the measured frame time.
+  // This prevents flooding the browser with more events than we need if the
+  // test is running very slow (such as on a VM).
+  int delay_us = mean_frame_time_us / kInputsPerFrame;
+  // Round delay_us down to nearest milliseconds.
+  int delay_ms = delay_us / 1000;
+  delay_ms = (delay_ms <= 0) ? 1 : delay_ms;
+
+  // Reset num_frames_ for actual test runs.
+  num_frames_ = kNumFrames;
+
+  // Run input latency test with each requested behavior.

[nduca, 2011/12/21 20:24:23]

This behaviors vs TEST_ distinction reminds me of the frame rate tests issue we
had with "gestures" versus "tests". Where we went was that 1 TEST_ produces 1
number, and we pipe that into the standard perf graphing infrastructure.

Does that learning not apply here for some reason? I would have expected a
different test for every interesting combination of flags rather than 1 test
with ~5 values.

[jbates, 2011/12/22 02:41:17]

Done.

+  for (size_t i = 0; i < behaviors.size(); ++i) {
+    // Sleep to allow the rendering pipeline to flush.
+    base::PlatformThread::Sleep(200);

[Paweł Hajdan Jr., 2011/12/21 09:50:29]

Shouldn't you rather wait for an event or something? Is the pipeline
_guaranteed_ to be flushed in 2 s? Why not 1s then? Or on a slow machine?

[jbates, 2011/12/21 19:34:18]

You're right, this was left-over from local testing. No sleep is needed here,
because the analysis already skips the first and last few frames. I also updated
the html to call gl.finish() before ending the test which will further reduce
the chance of data from a previous test showing up in the next trace.

+
+    test_flags_ = behaviors[i];
+    std::string url = GetUrl(test_flags_);
+    printf("=============================================================\n");
+    if (verbose_)
+      printf("Mode: %s\n", GetUrlModeString(i).c_str());
+    printf("URL: %s\n", url.c_str());
+
+    // Do the actual test with input events.
+    RunTestInternal(url, true, delay_ms);
+    latencies_[test_flags_] = CalculateLatency();
+  }
+
+  // Print summary if more than 1 behavior was tested in this run.

[nduca, 2011/12/21 20:24:23]

Is this for human consumption, or for consumption by a log parser? If the
latter, you might want to make that clear...

[jbates, 2011/12/22 02:41:17]

For human consumption, added a comment.

+  if (behaviors.size() > 1) {
+    printf("#############################################################\n");
+    printf("## %s\n", mode_.c_str());
+    if (verbose_) {
+      printf("Latency, behavior:\n");
+      for (size_t i = 0; i < behaviors.size(); ++i) {
+        printf("%.1f, %s%s%s%s\n", latencies_[behaviors[i]],
+               (i & kInputHeavy) ? "InputHeavy " : "",
+               (i & kInputDirty) ? "InputDirty " : "",
+               (i & kRafHeavy) ? "RafHeavy " : "",
+               (i & kPaintHeavy) ? "PaintHeavy " : "");
+      }
+    }
+    printf("Latencies for tests: ");
+    for (size_t i = 0; i < behaviors.size(); ++i) {
+      printf("%.1f%s", latencies_[behaviors[i]],
+             (i < behaviors.size() - 1) ? ", " : "");
+    }
+    printf("\n");
+    printf("#############################################################\n");
+  }
+}
+
+void LatencyTest::RunTestInternal(const std::string& test_url,
+                                  bool send_inputs,
+                                  int input_delay_ms) {
+  mouse_x_ = 0;
+
+  ASSERT_TRUE(tracing::BeginTracing("test_gpu,test_latency"));
+
+  ui_test_utils::NavigateToURLWithDisposition(
+      browser(), GURL(test_url), CURRENT_TAB,
+      ui_test_utils::BROWSER_TEST_NONE);
+
+  // Start sending mouse inputs.
+  if (send_inputs) {
+    timer_.Start(FROM_HERE, base::TimeDelta::FromMicroseconds(input_delay_ms),
+                 this, &LatencyTest::SendInput);
+  }
+
+  // Wait for message indicating the test has finished running.
+  ui_test_utils::DOMMessageQueue message_queue;
+  ASSERT_TRUE(message_queue.WaitForMessage(NULL));

[nduca, 2011/12/21 20:24:23]

Do we need any error handling here? Or is the idea that trace analysis will
miraculuously sort all this out for us?

[jbates, 2011/12/22 02:41:17]

The trace analysis does lots of error checking. Let me know if you see any gaps
in it.

+
+  timer_.Stop();
+
+  std::string json_events;
+  ASSERT_TRUE(tracing::EndTracing(&json_events));
+
+  analyzer_.reset(TraceAnalyzer::Create(json_events));
+  analyzer_->AssociateBeginEndEvents();
+  analyzer_->MergeAssociatedEventArgs();
+}
+
+double LatencyTest::CalculateLatency() {
+  TraceEventVector events;
+  if (mode_ == "webgl") {
+    // Search for three types of events in WebGL mode:
+    //  - onscreen swaps.
+    //  - DoClear calls that contain the mouse x coordinate.
+    //  - mouse events.
+    analyzer_->FindEvents(query_swaps_ || query_inputs_ ||
+                          query_blits_ || query_clears_, &events);
+  }
+  else if (mode_ == "software") {

[Paweł Hajdan Jr., 2011/12/21 09:50:29]

nit: Move to the previous line.

[jbates, 2011/12/21 19:34:18]

Done.

+    analyzer_->FindEvents(query_swaps_ || query_inputs_, &events);
+  } else {
+    CHECK(0) << "invalid mode";

[Paweł Hajdan Jr., 2011/12/21 09:50:29]

Oh, a CHECK? We usually do a NOTREACHED() in those cases.

[jbates, 2011/12/21 19:34:18]

Done.

+  }
+
+  if (verbose_)
+    PrintEvents(events);
+
+  int swap_count = 0;
+  size_t previous_blit_pos = 0;
+  swap_count = 0;
+  std::vector<int> latencies;
+  printf("Measured latency (in number of frames) for each frame:\n");

[nduca, 2011/12/21 20:24:23]

/me is confused about the output of this test. You're printf-ing always? I would
have expected it to pipe into the perf graphing system...

[jbates, 2011/12/22 02:41:17]

The only stuff that is parsed by the perf bots comes from the
perf_test::PrintResult* functions. The rest of the printfs are for human
consumption. If a perf test fails on the bots, you can go find the log to see
some basic output from the test and possibly reason about it. The only rule is
that the printf output doesn't look like the perf_test::PrintResult output so as
not to confuse the parser (discussed this with cmp).

+  for (size_t i = 0; i < events.size(); ++i) {

[nduca, 2011/12/21 20:24:23]

I'm a little surprise to see an actual loop in user code over the event list.
Does this suggest something about the trace analyzer system that we should
change/adjust?

[jbates, 2011/12/22 02:41:17]

I think it's just the nature of this test. It needs to rewind from specific
events one at a time and count things in between. You'll notice that I added
utility functions FindLastOf, FindClosest and CountMatches just for this test.
Let me know if you see other generic elements of this loop though -- it would be
great to simplify further.

+    if (query_swaps_.Evaluate(*events[i])) {
+      // Compositor context swap buffers.
+      ++swap_count;
+      // Don't analyze first few swaps, because they are filling the rendering
+      // pipeline and may be unstable. Latencies can be as high as 5 frames or
+      // so, so skip the first 6 frames to get more accurate results.
+      if (swap_count > 6) {
+        int mouse_x = 0;
+        if (mode_ == "webgl") {
+          // Trace backwards through the events to find the input event that
+          // matches the glClear that was presented by this SwapBuffers.
+
+          // Step 1: Find the last blit (which will be the WebGL blit).
+          size_t blit_pos = 0;
+          EXPECT_TRUE(FindLastOf(events, query_blits_, i, &blit_pos));
+          // Skip this SwapBuffers if the blit has already been consumed by a
+          // previous SwapBuffers. This means the current frame did not receive
+          // an update from WebGL.
+          EXPECT_GT(blit_pos, previous_blit_pos);
+          if (blit_pos == previous_blit_pos) {
+            if (verbose_)
+              printf(" %03d: ERROR\n", swap_count);
+            else
+              printf(" ERROR");
+            continue;
+          }
+          previous_blit_pos = blit_pos;
+
+          // Step 2: find the last clear from the WebGL blit. This will be the
+          // value of the latest mouse input that has affected this swap.
+          size_t clear_pos = 0;
+          EXPECT_TRUE(FindLastOf(events, query_clears_, blit_pos, &clear_pos));
+          mouse_x = events[clear_pos]->GetKnownArgAsInt("red");
+        } else if (mode_ == "software") {
+          // The software path gets the mouse_x directly from the DIB colors.
+          mouse_x = events[i]->GetKnownArgAsInt("color");
+        }
+
+        // Find the corresponding mouse input.
+        size_t input_pos = 0;
+        Query query_mouse_event = query_inputs_ &&
+            Query(EVENT_ARG, "x") == Query::Int(mouse_x);
+        EXPECT_TRUE(FindLastOf(events, query_mouse_event, i, &input_pos));
+
+        // Step 4: Find the nearest onscreen SwapBuffers to this input event.
+        size_t closest_swap = 0;
+        size_t second_closest_swap = 0;
+        EXPECT_TRUE(FindClosest(events, query_swaps_, input_pos,
+                                       &closest_swap, &second_closest_swap));
+        int latency = CountMatches(events, query_swaps_, closest_swap, i);
+        latencies.push_back(latency);
+        if (verbose_)
+          printf(" %03d: %d\n", swap_count, latency);
+        else
+          printf(" %d", latency);
+      }
+    }
+  }
+  printf("\n");
+
+  EXPECT_GT(latencies.size(), size_t(2));
+  if (latencies.size() <= size_t(2))
+    return 0.0;
+
+  double mean_latency = 0.0;
+  // Skip last couple latencies, because they could be unreliable.
+  size_t num_consider = latencies.size() - 2;
+  for (size_t i = 0; i < num_consider; ++i)
+    mean_latency += static_cast<double>(latencies[i]);
+  mean_latency /= static_cast<double>(num_consider);
+  printf("Mean latency = %f\n", mean_latency);
+
+  double mean_error = 0.0;
+  for (size_t i = 0; i < num_consider; ++i) {
+    double offset = fabs(mean_latency - static_cast<double>(latencies[i]));
+    mean_error = (offset > mean_error) ? offset : mean_error;
+  }
+
+  std::string trace_name = GetTraceName(test_flags_);
+  std::string mean_and_error = base::StringPrintf("%f,%f", mean_latency,
+                                                  mean_error);
+  perf_test::PrintResultMeanAndError(mode_, "", trace_name, mean_and_error,
+                                     "frames", true);
+  return mean_latency;
+}
+
+// For manual testing only, run all input latency tests and print summary.
+IN_PROC_BROWSER_TEST_F(LatencyTest, DISABLED_WebGLLatencyAll) {
+  RunTest("webgl", GetAllBehaviors());
+}
+
+// For manual testing only, run all input latency tests and print summary.
+IN_PROC_BROWSER_TEST_F(LatencyTest, DISABLED_SoftwareLatencyAll) {
+  RunTest("software", GetAllBehaviors());
+}
+
+IN_PROC_BROWSER_TEST_F(LatencyTest, WebGLLatencySelect) {
+  std::vector<int> behaviors;
+  behaviors.push_back(0);
+  behaviors.push_back(kInputHeavy);
+  behaviors.push_back(kInputHeavy | kInputDirty | kRafHeavy);
+  behaviors.push_back(kInputDirty | kPaintHeavy);
+  behaviors.push_back(kInputDirty | kRafHeavy | kPaintHeavy);
+  behaviors.push_back(kInputDirty | kInputHeavy | kRafHeavy | kPaintHeavy);
+  RunTest("webgl", behaviors);
+}
+
+IN_PROC_BROWSER_TEST_F(LatencyTest, SoftwareLatencySelect) {
+  std::vector<int> behaviors;
+  behaviors.push_back(0);
+  behaviors.push_back(kInputHeavy);
+  behaviors.push_back(kInputHeavy | kInputDirty | kRafHeavy);
+  behaviors.push_back(kInputDirty | kPaintHeavy);
+  behaviors.push_back(kInputDirty | kRafHeavy | kPaintHeavy);
+  behaviors.push_back(kInputDirty | kInputHeavy | kRafHeavy | kPaintHeavy);
+  RunTest("software", behaviors);
+}
+
+}  // namespace anonymous