cc: Remove retro frames from scheduler.

cc/scheduler/begin_frame_source.cc

Index: cc/scheduler/begin_frame_source.cc
diff --git a/cc/scheduler/begin_frame_source.cc b/cc/scheduler/begin_frame_source.cc
index e0bc5e0a48a0133f35bcf389b05917e5f3c8bdd3..b429ba580de54d8c10d9997d4b9b88d1c7d5514f 100644
--- a/cc/scheduler/begin_frame_source.cc
+++ b/cc/scheduler/begin_frame_source.cc
@@ -24,38 +24,6 @@ namespace {
 static const double kDoubleTickDivisor = 2.0;
 }
 
-// BeginFrameObserverBase -----------------------------------------------
-BeginFrameObserverBase::BeginFrameObserverBase()
-    : last_begin_frame_args_(), dropped_begin_frame_args_(0) {
-}
-
-const BeginFrameArgs& BeginFrameObserverBase::LastUsedBeginFrameArgs() const {
-  return last_begin_frame_args_;
-}
-void BeginFrameObserverBase::OnBeginFrame(const BeginFrameArgs& args) {
-  DEBUG_FRAMES("BeginFrameObserverBase::OnBeginFrame",
-               "last args",
-               last_begin_frame_args_.AsValue(),
-               "new args",
-               args.AsValue());
-  DCHECK(args.IsValid());
-  DCHECK(args.frame_time >= last_begin_frame_args_.frame_time);
-  bool used = OnBeginFrameDerivedImpl(args);
-  if (used) {
-    last_begin_frame_args_ = args;
-  } else {
-    ++dropped_begin_frame_args_;
-  }
-}
-
-void BeginFrameObserverBase::AsValueInto(
-    base::trace_event::TracedValue* dict) const {
-  dict->BeginDictionary("last_begin_frame_args_");
-  last_begin_frame_args_.AsValueInto(dict);
-  dict->EndDictionary();
-  dict->SetInteger("dropped_begin_frame_args_", dropped_begin_frame_args_);
-}
-
 // BeginFrameSourceBase ------------------------------------------------------
 BeginFrameSourceBase::BeginFrameSourceBase()
     : paused_(false), inside_as_value_into_(false) {}
@@ -174,9 +142,8 @@ void BackToBackBeginFrameSource::BeginFrame() {
   CallOnBeginFrame(args);
 }
 
-void BackToBackBeginFrameSource::DidFinishFrame(size_t remaining_frames) {
-  BeginFrameSourceBase::DidFinishFrame(remaining_frames);
-  if (needs_begin_frames() && remaining_frames == 0)
+void BackToBackBeginFrameSource::DidFinishFrame(BeginFrameObserver* obs) {
+  if (needs_begin_frames())
     PostBeginFrame();

[enne (OOO), 2016/04/14 23:02:26]

Hmm.  Should this only post a begin frame to the observer that finished?
Otherwise, if you have two observers, when one finishes, you'll post two new
begin frames?

 }
 
@@ -219,6 +186,18 @@ BeginFrameArgs SyntheticBeginFrameSource::CreateBeginFrameArgs(
 }
 
 // BeginFrameSource support
+void SyntheticBeginFrameSource::DidFinishFrame(BeginFrameObserver* obs) {
+  BeginFrameArgs args = CreateBeginFrameArgs(
+      time_source_->NextTickTime() - time_source_->Interval(),
+      BeginFrameArgs::MISSED);
+  BeginFrameArgs last_args = obs->LastUsedBeginFrameArgs();
+  if (!last_args.IsValid() ||
+      (args.frame_time >
+       last_args.frame_time + args.interval / kDoubleTickDivisor)) {
+    obs->OnBeginFrame(args);
+  }
+}
+
 void SyntheticBeginFrameSource::AddObserver(BeginFrameObserver* obs) {
   BeginFrameSourceBase::AddObserver(obs);
   BeginFrameArgs args = CreateBeginFrameArgs(