cc: Add MainAndImplFrameTimeDelta UMA.

Records how often the main and impl threads are synchronized
when the compositor draws with a new active tree.

Some DCHECKS are disabled for the synchronous compositor
because draws can come in at any time or not at all.

BUG=582749
CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel

Review URL: https://codereview.chromium.org/1681393003

Cr-Commit-Position: refs/heads/master@{#376628}

11 files changed, 137 insertions, 40 deletions

diff --git a/cc/scheduler/compositor_timing_history.cc b/cc/scheduler/compositor_timing_history.cc
index f546062..ab1cd04 100644
--- a/cc/scheduler/compositor_timing_history.cc
+++ b/cc/scheduler/compositor_timing_history.cc
@@ -50,6 +50,9 @@ class CompositorTimingHistory::UMAReporter {
                                base::TimeDelta estimate,
                                bool affects_estimate) = 0;
   virtual void AddSwapToAckLatency(base::TimeDelta duration) = 0;
+
+  // Synchronization measurements
+  virtual void AddMainAndImplFrameTimeDelta(base::TimeDelta delta) = 0;
 };
 
 namespace {
@@ -217,6 +220,11 @@ class RendererUMAReporter : public CompositorTimingHistory::UMAReporter {
     UMA_HISTOGRAM_CUSTOM_TIMES_MICROS("Scheduling.Renderer.SwapToAckLatency",
                                       duration);
   }
+
+  void AddMainAndImplFrameTimeDelta(base::TimeDelta delta) override {
+    UMA_HISTOGRAM_CUSTOM_TIMES_MICROS(
+        "Scheduling.Renderer.MainAndImplFrameTimeDelta", delta);
+  }
 };
 
 class BrowserUMAReporter : public CompositorTimingHistory::UMAReporter {
@@ -298,6 +306,11 @@ class BrowserUMAReporter : public CompositorTimingHistory::UMAReporter {
     UMA_HISTOGRAM_CUSTOM_TIMES_MICROS("Scheduling.Browser.SwapToAckLatency",
                                       duration);
   }
+
+  void AddMainAndImplFrameTimeDelta(base::TimeDelta delta) override {
+    UMA_HISTOGRAM_CUSTOM_TIMES_MICROS(
+        "Scheduling.Browser.MainAndImplFrameTimeDelta", delta);
+  }
 };
 
 class NullUMAReporter : public CompositorTimingHistory::UMAReporter {
@@ -332,14 +345,18 @@ class NullUMAReporter : public CompositorTimingHistory::UMAReporter {
                        base::TimeDelta estimate,
                        bool affects_estimate) override {}
   void AddSwapToAckLatency(base::TimeDelta duration) override {}
+  void AddMainAndImplFrameTimeDelta(base::TimeDelta delta) override {}
 };
 
 }  // namespace
 
 CompositorTimingHistory::CompositorTimingHistory(
+    bool using_synchronous_renderer_compositor,
     UMACategory uma_category,
     RenderingStatsInstrumentation* rendering_stats_instrumentation)
-    : enabled_(false),
+    : using_synchronous_renderer_compositor_(
+          using_synchronous_renderer_compositor),
+      enabled_(false),
       did_send_begin_main_frame_(false),
       begin_main_frame_needed_continuously_(false),
       begin_main_frame_committing_continuously_(false),
@@ -478,6 +495,12 @@ base::TimeDelta CompositorTimingHistory::DrawDurationEstimate() const {
   return draw_duration_history_.Percentile(kDrawEstimationPercentile);
 }
 
+void CompositorTimingHistory::DidCreateAndInitializeOutputSurface() {
+  // After we get a new output surface, we won't get a spurious
+  // swap ack from the old output surface.
+  swap_start_time_ = base::TimeTicks();
+}
+
 void CompositorTimingHistory::WillBeginImplFrame(
     bool new_active_tree_is_likely) {
   // The check for whether a BeginMainFrame was sent anytime between two
@@ -505,10 +528,15 @@ void CompositorTimingHistory::BeginImplFrameNotExpectedSoon() {
   SetCompositorDrawingContinuously(false);
 }
 
-void CompositorTimingHistory::WillBeginMainFrame(bool on_critical_path) {
+void CompositorTimingHistory::WillBeginMainFrame(
+    bool on_critical_path,
+    base::TimeTicks main_frame_time) {
   DCHECK_EQ(base::TimeTicks(), begin_main_frame_sent_time_);
+  DCHECK_EQ(base::TimeTicks(), begin_main_frame_frame_time_);
+
   begin_main_frame_on_critical_path_ = on_critical_path;
   begin_main_frame_sent_time_ = Now();
+  begin_main_frame_frame_time_ = main_frame_time;
 
   did_send_begin_main_frame_ = true;
   SetBeginMainFrameNeededContinuously(true);
@@ -524,11 +552,15 @@ void CompositorTimingHistory::BeginMainFrameStarted(
 void CompositorTimingHistory::BeginMainFrameAborted() {
   SetBeginMainFrameCommittingContinuously(false);
   DidBeginMainFrame();
+  begin_main_frame_frame_time_ = base::TimeTicks();
 }
 
 void CompositorTimingHistory::DidCommit() {
+  DCHECK_EQ(base::TimeTicks(), pending_tree_main_frame_time_);
   SetBeginMainFrameCommittingContinuously(true);
   DidBeginMainFrame();
+  pending_tree_main_frame_time_ = begin_main_frame_frame_time_;
+  begin_main_frame_frame_time_ = base::TimeTicks();
 }
 
 void CompositorTimingHistory::DidBeginMainFrame() {
@@ -666,7 +698,13 @@ void CompositorTimingHistory::DidActivate() {
   if (enabled_)
     activate_duration_history_.InsertSample(activate_duration);
 
+  // The synchronous compositor doesn't necessarily draw every new active tree.
+  if (!using_synchronous_renderer_compositor_)
+    DCHECK_EQ(base::TimeTicks(), active_tree_main_frame_time_);
+  active_tree_main_frame_time_ = pending_tree_main_frame_time_;
+
   activate_start_time_ = base::TimeTicks();
+  pending_tree_main_frame_time_ = base::TimeTicks();
 }
 
 void CompositorTimingHistory::WillDraw() {
@@ -674,7 +712,13 @@ void CompositorTimingHistory::WillDraw() {
   draw_start_time_ = Now();
 }
 
-void CompositorTimingHistory::DidDraw(bool used_new_active_tree) {
+void CompositorTimingHistory::DrawAborted() {
+  active_tree_main_frame_time_ = base::TimeTicks();
+}
+
+void CompositorTimingHistory::DidDraw(bool used_new_active_tree,
+                                      bool main_thread_missed_last_deadline,
+                                      base::TimeTicks impl_frame_time) {
   DCHECK_NE(base::TimeTicks(), draw_start_time_);
   base::TimeTicks draw_end_time = Now();
   base::TimeDelta draw_duration = draw_end_time - draw_start_time_;
@@ -699,13 +743,26 @@ void CompositorTimingHistory::DidDraw(bool used_new_active_tree) {
   }
   draw_end_time_prev_ = draw_end_time;
 
-  if (begin_main_frame_committing_continuously_ && used_new_active_tree) {
-    if (!new_active_tree_draw_end_time_prev_.is_null()) {
-      base::TimeDelta draw_interval =
-          draw_end_time - new_active_tree_draw_end_time_prev_;
-      uma_reporter_->AddCommitInterval(draw_interval);
+  if (used_new_active_tree) {
+    DCHECK_NE(base::TimeTicks(), active_tree_main_frame_time_);
+    base::TimeDelta main_and_impl_delta =
+        impl_frame_time - active_tree_main_frame_time_;
+    DCHECK_GE(main_and_impl_delta, base::TimeDelta());
+    if (!using_synchronous_renderer_compositor_) {
+      DCHECK_EQ(main_thread_missed_last_deadline,
+                !main_and_impl_delta.is_zero());
+    }
+    uma_reporter_->AddMainAndImplFrameTimeDelta(main_and_impl_delta);
+    active_tree_main_frame_time_ = base::TimeTicks();
+
+    if (begin_main_frame_committing_continuously_) {
+      if (!new_active_tree_draw_end_time_prev_.is_null()) {
+        base::TimeDelta draw_interval =
+            draw_end_time - new_active_tree_draw_end_time_prev_;
+        uma_reporter_->AddCommitInterval(draw_interval);
+      }
+      new_active_tree_draw_end_time_prev_ = draw_end_time;
     }
-    new_active_tree_draw_end_time_prev_ = draw_end_time;
   }
 
   draw_start_time_ = base::TimeTicks();
@@ -723,8 +780,4 @@ void CompositorTimingHistory::DidSwapBuffersComplete() {
   swap_start_time_ = base::TimeTicks();
 }
 
-void CompositorTimingHistory::DidSwapBuffersReset() {
-  swap_start_time_ = base::TimeTicks();
-}
-
 }  // namespace cc
diff --git a/cc/scheduler/compositor_timing_history.h b/cc/scheduler/compositor_timing_history.h
index 11dfc00..a7c58dd 100644
--- a/cc/scheduler/compositor_timing_history.h
+++ b/cc/scheduler/compositor_timing_history.h
@@ -29,6 +29,7 @@ class CC_EXPORT CompositorTimingHistory {
   class UMAReporter;
 
   CompositorTimingHistory(
+      bool using_synchronous_renderer_compositor,
       UMACategory uma_category,
       RenderingStatsInstrumentation* rendering_stats_instrumentation);
   virtual ~CompositorTimingHistory();
@@ -49,12 +50,16 @@ class CC_EXPORT CompositorTimingHistory {
   virtual base::TimeDelta ActivateDurationEstimate() const;
   virtual base::TimeDelta DrawDurationEstimate() const;
 
+  // State that affects when events should be expected/recorded/reported.
   void SetRecordingEnabled(bool enabled);
+  void DidCreateAndInitializeOutputSurface();
 
+  // Events to be timed.
   void WillBeginImplFrame(bool new_active_tree_is_likely);
   void WillFinishImplFrame(bool needs_redraw);
   void BeginImplFrameNotExpectedSoon();
-  void WillBeginMainFrame(bool on_critical_path);
+  void WillBeginMainFrame(bool on_critical_path,
+                          base::TimeTicks main_frame_time);
   void BeginMainFrameStarted(base::TimeTicks main_thread_start_time);
   void BeginMainFrameAborted();
   void DidCommit();
@@ -63,11 +68,13 @@ class CC_EXPORT CompositorTimingHistory {
   void ReadyToActivate();
   void WillActivate();
   void DidActivate();
+  void DrawAborted();
   void WillDraw();
-  void DidDraw(bool used_new_active_tree);
+  void DidDraw(bool used_new_active_tree,
+               bool main_thread_missed_last_deadline,
+               base::TimeTicks impl_frame_time);
   void DidSwapBuffers();
   void DidSwapBuffersComplete();
-  void DidSwapBuffersReset();
 
  protected:
   void DidBeginMainFrame();
@@ -79,6 +86,7 @@ class CC_EXPORT CompositorTimingHistory {
   static scoped_ptr<UMAReporter> CreateUMAReporter(UMACategory category);
   virtual base::TimeTicks Now() const;
 
+  bool using_synchronous_renderer_compositor_;
   bool enabled_;
 
   // Used to calculate frame rates of Main and Impl threads.
@@ -101,11 +109,14 @@ class CC_EXPORT CompositorTimingHistory {
   RollingTimeDeltaHistory draw_duration_history_;
 
   bool begin_main_frame_on_critical_path_;
+  base::TimeTicks begin_main_frame_frame_time_;
   base::TimeTicks begin_main_frame_sent_time_;
   base::TimeTicks begin_main_frame_start_time_;
   base::TimeTicks begin_main_frame_end_time_;
+  base::TimeTicks pending_tree_main_frame_time_;
   base::TimeTicks prepare_tiles_start_time_;
   base::TimeTicks activate_start_time_;
+  base::TimeTicks active_tree_main_frame_time_;
   base::TimeTicks draw_start_time_;
   base::TimeTicks swap_start_time_;
 
diff --git a/cc/scheduler/compositor_timing_history_unittest.cc b/cc/scheduler/compositor_timing_history_unittest.cc
index 900367f..f57d443 100644
--- a/cc/scheduler/compositor_timing_history_unittest.cc
+++ b/cc/scheduler/compositor_timing_history_unittest.cc
@@ -17,7 +17,8 @@ class TestCompositorTimingHistory : public CompositorTimingHistory {
  public:
   TestCompositorTimingHistory(CompositorTimingHistoryTest* test,
                               RenderingStatsInstrumentation* rendering_stats)
-      : CompositorTimingHistory(NULL_UMA, rendering_stats), test_(test) {}
+      : CompositorTimingHistory(false, NULL_UMA, rendering_stats),
+        test_(test) {}
 
  protected:
   base::TimeTicks Now() const override;
@@ -68,7 +69,7 @@ TEST_F(CompositorTimingHistoryTest, AllSequential_Commit) {
   base::TimeDelta activate_duration = base::TimeDelta::FromMilliseconds(4);
   base::TimeDelta draw_duration = base::TimeDelta::FromMilliseconds(5);
 
-  timing_history_.WillBeginMainFrame(true);
+  timing_history_.WillBeginMainFrame(true, Now());
   AdvanceNowBy(begin_main_frame_queue_duration);
   timing_history_.BeginMainFrameStarted(Now());
   AdvanceNowBy(begin_main_frame_start_to_commit_duration);
@@ -87,7 +88,7 @@ TEST_F(CompositorTimingHistoryTest, AllSequential_Commit) {
   AdvanceNowBy(one_second);
   timing_history_.WillDraw();
   AdvanceNowBy(draw_duration);
-  timing_history_.DidDraw(true);
+  timing_history_.DidDraw(true, true, Now());
 
   EXPECT_EQ(begin_main_frame_queue_duration,
             timing_history_.BeginMainFrameQueueDurationCriticalEstimate());
@@ -126,7 +127,7 @@ TEST_F(CompositorTimingHistoryTest, AllSequential_BeginMainFrameAborted) {
   base::TimeDelta activate_duration = base::TimeDelta::FromMilliseconds(4);
   base::TimeDelta draw_duration = base::TimeDelta::FromMilliseconds(5);
 
-  timing_history_.WillBeginMainFrame(true);
+  timing_history_.WillBeginMainFrame(false, Now());
   AdvanceNowBy(begin_main_frame_queue_duration);
   timing_history_.BeginMainFrameStarted(Now());
   AdvanceNowBy(begin_main_frame_start_to_commit_duration);
@@ -146,9 +147,9 @@ TEST_F(CompositorTimingHistoryTest, AllSequential_BeginMainFrameAborted) {
   AdvanceNowBy(one_second);
   timing_history_.WillDraw();
   AdvanceNowBy(draw_duration);
-  timing_history_.DidDraw(true);
+  timing_history_.DidDraw(false, false, Now());
 
-  EXPECT_EQ(begin_main_frame_queue_duration,
+  EXPECT_EQ(base::TimeDelta(),
             timing_history_.BeginMainFrameQueueDurationCriticalEstimate());
   EXPECT_EQ(begin_main_frame_queue_duration,
             timing_history_.BeginMainFrameQueueDurationNotCriticalEstimate());
@@ -179,13 +180,13 @@ TEST_F(CompositorTimingHistoryTest, BeginMainFrame_CriticalFaster) {
   base::TimeDelta begin_main_frame_start_to_commit_duration =
       base::TimeDelta::FromMilliseconds(1);
 
-  timing_history_.WillBeginMainFrame(true);
+  timing_history_.WillBeginMainFrame(true, Now());
   AdvanceNowBy(begin_main_frame_queue_duration_critical);
   timing_history_.BeginMainFrameStarted(Now());
   AdvanceNowBy(begin_main_frame_start_to_commit_duration);
   timing_history_.BeginMainFrameAborted();
 
-  timing_history_.WillBeginMainFrame(false);
+  timing_history_.WillBeginMainFrame(false, Now());
   AdvanceNowBy(begin_main_frame_queue_duration_not_critical);
   timing_history_.BeginMainFrameStarted(Now());
   AdvanceNowBy(begin_main_frame_start_to_commit_duration);
@@ -219,7 +220,7 @@ TEST_F(CompositorTimingHistoryTest, BeginMainFrames_OldCriticalSlower) {
       base::TimeDelta::FromMilliseconds(1);
 
   // A single critical frame that is slow.
-  timing_history_.WillBeginMainFrame(true);
+  timing_history_.WillBeginMainFrame(true, Now());
   AdvanceNowBy(begin_main_frame_queue_duration_critical);
   timing_history_.BeginMainFrameStarted(Now());
   AdvanceNowBy(begin_main_frame_start_to_commit_duration);
@@ -228,7 +229,7 @@ TEST_F(CompositorTimingHistoryTest, BeginMainFrames_OldCriticalSlower) {
 
   // A bunch of faster non critical frames that are newer.
   for (int i = 0; i < 100; i++) {
-    timing_history_.WillBeginMainFrame(false);
+    timing_history_.WillBeginMainFrame(false, Now());
     AdvanceNowBy(begin_main_frame_queue_duration_not_critical);
     timing_history_.BeginMainFrameStarted(Now());
     AdvanceNowBy(begin_main_frame_start_to_commit_duration);
@@ -265,7 +266,7 @@ TEST_F(CompositorTimingHistoryTest, BeginMainFrames_NewCriticalSlower) {
       base::TimeDelta::FromMilliseconds(1);
 
   // A single non critical frame that is fast.
-  timing_history_.WillBeginMainFrame(false);
+  timing_history_.WillBeginMainFrame(false, Now());
   AdvanceNowBy(begin_main_frame_queue_duration_not_critical);
   timing_history_.BeginMainFrameStarted(Now());
   AdvanceNowBy(begin_main_frame_start_to_commit_duration);
@@ -273,7 +274,7 @@ TEST_F(CompositorTimingHistoryTest, BeginMainFrames_NewCriticalSlower) {
 
   // A bunch of slower critical frames that are newer.
   for (int i = 0; i < 100; i++) {
-    timing_history_.WillBeginMainFrame(true);
+    timing_history_.WillBeginMainFrame(true, Now());
     AdvanceNowBy(begin_main_frame_queue_duration_critical);
     timing_history_.BeginMainFrameStarted(Now());
     AdvanceNowBy(begin_main_frame_start_to_commit_duration);
diff --git a/cc/scheduler/scheduler.cc b/cc/scheduler/scheduler.cc
index 499fae7..61607de 100644
--- a/cc/scheduler/scheduler.cc
+++ b/cc/scheduler/scheduler.cc
@@ -249,8 +249,8 @@ void Scheduler::DidCreateAndInitializeOutputSurface() {
   TRACE_EVENT0("cc", "Scheduler::DidCreateAndInitializeOutputSurface");
   DCHECK(!observing_frame_source_);
   DCHECK(begin_impl_frame_deadline_task_.IsCancelled());
-  compositor_timing_history_->DidSwapBuffersReset();
   state_machine_.DidCreateAndInitializeOutputSurface();
+  compositor_timing_history_->DidCreateAndInitializeOutputSurface();
   UpdateCompositorTimingHistoryRecordingEnabled();
   ProcessScheduledActions();
 }
@@ -663,21 +663,29 @@ void Scheduler::OnBeginImplFrameDeadline() {
 void Scheduler::DrawAndSwapIfPossible() {
   bool drawing_with_new_active_tree =
       state_machine_.active_tree_needs_first_draw();
+  bool main_thread_missed_last_deadline =
+      state_machine_.main_thread_missed_last_deadline();
   compositor_timing_history_->WillDraw();
   state_machine_.WillDraw();
   DrawResult result = client_->ScheduledActionDrawAndSwapIfPossible();
   state_machine_.DidDraw(result);
-  compositor_timing_history_->DidDraw(drawing_with_new_active_tree);
+  compositor_timing_history_->DidDraw(
+      drawing_with_new_active_tree, main_thread_missed_last_deadline,
+      begin_impl_frame_tracker_.DangerousMethodCurrentOrLast().frame_time);
 }
 
 void Scheduler::DrawAndSwapForced() {
   bool drawing_with_new_active_tree =
       state_machine_.active_tree_needs_first_draw();
+  bool main_thread_missed_last_deadline =
+      state_machine_.main_thread_missed_last_deadline();
   compositor_timing_history_->WillDraw();
   state_machine_.WillDraw();
   DrawResult result = client_->ScheduledActionDrawAndSwapForced();
   state_machine_.DidDraw(result);
-  compositor_timing_history_->DidDraw(drawing_with_new_active_tree);
+  compositor_timing_history_->DidDraw(
+      drawing_with_new_active_tree, main_thread_missed_last_deadline,
+      begin_impl_frame_tracker_.DangerousMethodCurrentOrLast().frame_time);
 }
 
 void Scheduler::SetDeferCommits(bool defer_commits) {
@@ -710,7 +718,8 @@ void Scheduler::ProcessScheduledActions() {
         break;
       case SchedulerStateMachine::ACTION_SEND_BEGIN_MAIN_FRAME:
         compositor_timing_history_->WillBeginMainFrame(
-            begin_main_frame_args_.on_critical_path);
+            begin_main_frame_args_.on_critical_path,
+            begin_main_frame_args_.frame_time);
         state_machine_.WillSendBeginMainFrame();
         // TODO(brianderson): Pass begin_main_frame_args_ directly to client.
         client_->ScheduledActionSendBeginMainFrame(begin_main_frame_args_);
@@ -748,6 +757,7 @@ void Scheduler::ProcessScheduledActions() {
         // No action is actually performed, but this allows the state machine to
         // drain the pipeline without actually drawing.
         state_machine_.AbortDrawAndSwap();
+        compositor_timing_history_->DrawAborted();
         break;
       }
       case SchedulerStateMachine::ACTION_BEGIN_OUTPUT_SURFACE_CREATION:
diff --git a/cc/scheduler/scheduler_state_machine.cc b/cc/scheduler/scheduler_state_machine.cc
index a1314fa..23715ae 100644
--- a/cc/scheduler/scheduler_state_machine.cc
+++ b/cc/scheduler/scheduler_state_machine.cc
@@ -613,7 +613,6 @@ void SchedulerStateMachine::WillCommit(bool commit_has_no_updates) {
       forced_redraw_state_ == FORCED_REDRAW_STATE_WAITING_FOR_DRAW) {
     DCHECK(!has_pending_tree_);
     needs_redraw_ = true;
-    active_tree_needs_first_draw_ = true;
   }
 
   // This post-commit work is common to both completed and aborted commits.
diff --git a/cc/scheduler/scheduler_unittest.cc b/cc/scheduler/scheduler_unittest.cc
index 8b8193b..8989e04 100644
--- a/cc/scheduler/scheduler_unittest.cc
+++ b/cc/scheduler/scheduler_unittest.cc
@@ -263,7 +263,8 @@ class SchedulerTest : public testing::Test {
     }
 
     scoped_ptr<FakeCompositorTimingHistory> fake_compositor_timing_history =
-        FakeCompositorTimingHistory::Create();
+        FakeCompositorTimingHistory::Create(
+            scheduler_settings_.using_synchronous_renderer_compositor);
     fake_compositor_timing_history_ = fake_compositor_timing_history.get();
 
     scheduler_ = TestScheduler::Create(
diff --git a/cc/test/scheduler_test_common.cc b/cc/test/scheduler_test_common.cc
index b6b1b2b..ef760d2 100644
--- a/cc/test/scheduler_test_common.cc
+++ b/cc/test/scheduler_test_common.cc
@@ -67,16 +67,20 @@ TestSyntheticBeginFrameSource::TestSyntheticBeginFrameSource(
 TestSyntheticBeginFrameSource::~TestSyntheticBeginFrameSource() {
 }
 
-scoped_ptr<FakeCompositorTimingHistory> FakeCompositorTimingHistory::Create() {
+scoped_ptr<FakeCompositorTimingHistory> FakeCompositorTimingHistory::Create(
+    bool using_synchronous_renderer_compositor) {
   scoped_ptr<RenderingStatsInstrumentation> rendering_stats_instrumentation =
       RenderingStatsInstrumentation::Create();
   return make_scoped_ptr(new FakeCompositorTimingHistory(
+      using_synchronous_renderer_compositor,
       std::move(rendering_stats_instrumentation)));
 }
 
 FakeCompositorTimingHistory::FakeCompositorTimingHistory(
+    bool using_synchronous_renderer_compositor,
     scoped_ptr<RenderingStatsInstrumentation> rendering_stats_instrumentation)
-    : CompositorTimingHistory(CompositorTimingHistory::NULL_UMA,
+    : CompositorTimingHistory(using_synchronous_renderer_compositor,
+                              CompositorTimingHistory::NULL_UMA,
                               rendering_stats_instrumentation.get()),
       rendering_stats_instrumentation_owned_(
           std::move(rendering_stats_instrumentation)) {}
diff --git a/cc/test/scheduler_test_common.h b/cc/test/scheduler_test_common.h
index 3993c9f..d442aca 100644
--- a/cc/test/scheduler_test_common.h
+++ b/cc/test/scheduler_test_common.h
@@ -164,7 +164,8 @@ class TestSyntheticBeginFrameSource : public SyntheticBeginFrameSource {
 
 class FakeCompositorTimingHistory : public CompositorTimingHistory {
  public:
-  static scoped_ptr<FakeCompositorTimingHistory> Create();
+  static scoped_ptr<FakeCompositorTimingHistory> Create(
+      bool using_synchronous_renderer_compositor);
   ~FakeCompositorTimingHistory() override;
 
   void SetAllEstimatesTo(base::TimeDelta duration);
@@ -190,7 +191,8 @@ class FakeCompositorTimingHistory : public CompositorTimingHistory {
   base::TimeDelta DrawDurationEstimate() const override;
 
  protected:
-  FakeCompositorTimingHistory(scoped_ptr<RenderingStatsInstrumentation>
+  FakeCompositorTimingHistory(bool using_synchronous_renderer_compositor,
+                              scoped_ptr<RenderingStatsInstrumentation>
                                   rendering_stats_instrumentation_owned);
 
   scoped_ptr<RenderingStatsInstrumentation>
diff --git a/cc/trees/proxy_impl.cc b/cc/trees/proxy_impl.cc
index f9a1eab..aefd847 100644
--- a/cc/trees/proxy_impl.cc
+++ b/cc/trees/proxy_impl.cc
@@ -74,8 +74,10 @@ ProxyImpl::ProxyImpl(ChannelImpl* channel_impl,
       layer_tree_host->settings().ToSchedulerSettings());
 
   scoped_ptr<CompositorTimingHistory> compositor_timing_history(
-      new CompositorTimingHistory(CompositorTimingHistory::RENDERER_UMA,
-                                  rendering_stats_instrumentation_));
+      new CompositorTimingHistory(
+          scheduler_settings.using_synchronous_renderer_compositor,
+          CompositorTimingHistory::RENDERER_UMA,
+          rendering_stats_instrumentation_));
 
   scheduler_ = Scheduler::Create(this, scheduler_settings, layer_tree_host_id_,
                                  task_runner_provider_->ImplThreadTaskRunner(),
diff --git a/cc/trees/single_thread_proxy.cc b/cc/trees/single_thread_proxy.cc
index 5898c7a..571c78d 100644
--- a/cc/trees/single_thread_proxy.cc
+++ b/cc/trees/single_thread_proxy.cc
@@ -67,6 +67,7 @@ void SingleThreadProxy::Start(
 
     scoped_ptr<CompositorTimingHistory> compositor_timing_history(
         new CompositorTimingHistory(
+            scheduler_settings.using_synchronous_renderer_compositor,
             CompositorTimingHistory::BROWSER_UMA,
             layer_tree_host_->rendering_stats_instrumentation()));
 
diff --git a/tools/metrics/histograms/histograms.xml b/tools/metrics/histograms/histograms.xml
index 89ec16f..cf050a1 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -43581,6 +43581,18 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Scheduling.MainAndImplFrameTimeDelta" units="microseconds">
+  <owner>brianderson@chromium.org</owner>
+  <summary>
+    Recorded every time the compositor draws with a new active tree. A value of
+    0 indicates the main-side started and finished within the same frame
+    interval as the impl-side. Positive values correspond to how old any
+    main-side updates are compared to the impl-side updates. If there are no
+    mid-frame updates, this metric is a good proxy for how well the main and
+    impl threads are synchronized.
+  </summary>
+</histogram>
+
 <histogram name="Scheduling.PrepareTilesDuration" units="microseconds">
   <owner>brianderson@chromium.org</owner>
   <summary>
@@ -83318,6 +83330,7 @@ To add a new entry, add it with any value and run test to compute valid value.
   <affected-histogram name="Scheduling.BeginMainFrameToCommitDuration"/>
   <affected-histogram name="Scheduling.CommitToReadyToActivateDuration"/>
   <affected-histogram name="Scheduling.DrawDuration"/>
+  <affected-histogram name="Scheduling.MainAndImplFrameTimeDelta"/>
   <affected-histogram name="Scheduling.PrepareTilesDuration"/>
   <affected-histogram name="Scheduling.SwapToAckLatency"/>
 </histogram_suffixes>