cc: Make BackToBackBeginFrameSource a SyntheticBeginFrameSource.

cc/test/fake_external_begin_frame_source.cc

Index: cc/test/fake_external_begin_frame_source.cc
diff --git a/cc/test/fake_external_begin_frame_source.cc b/cc/test/fake_external_begin_frame_source.cc
index 7dc4bef3073e4b90d6d529e39cf8b570218c58a7..9beff1540566e6df3001846178205339ca1ee42d 100644
--- a/cc/test/fake_external_begin_frame_source.cc
+++ b/cc/test/fake_external_begin_frame_source.cc
@@ -12,8 +12,11 @@
 
 namespace cc {
 
-FakeExternalBeginFrameSource::FakeExternalBeginFrameSource(double refresh_rate)
-    : milliseconds_per_frame_(1000.0 / refresh_rate),
+FakeExternalBeginFrameSource::FakeExternalBeginFrameSource(
+    double refresh_rate,
+    bool tick_automatically)
+    : tick_automatically_(tick_automatically),
+      milliseconds_per_frame_(1000.0 / refresh_rate),
       weak_ptr_factory_(this) {
   DetachFromThread();
 }
@@ -22,20 +25,47 @@ FakeExternalBeginFrameSource::~FakeExternalBeginFrameSource() {
   DCHECK(CalledOnValidThread());
 }
 
-void FakeExternalBeginFrameSource::OnNeedsBeginFramesChanged(
-    bool needs_begin_frames) {
-  DCHECK(CalledOnValidThread());
-  if (needs_begin_frames) {
+void FakeExternalBeginFrameSource::SetPaused(bool paused) {
+  if (paused != paused_) {
+    paused_ = paused;
+    std::set<BeginFrameObserver*> observers(observers_);
+    for (auto* obs : observers)
+      obs->OnBeginFrameSourcePausedChanged(paused_);
+  }
+}
+
+void FakeExternalBeginFrameSource::AddObserver(BeginFrameObserver* obs) {
+  DCHECK(obs);
+  DCHECK(observers_.find(obs) == observers_.end());
+
+  bool observers_was_empty = observers_.empty();
+  observers_.insert(obs);
+  obs->OnBeginFrameSourcePausedChanged(paused_);
+  if (observers_was_empty && tick_automatically_)
     PostTestOnBeginFrame();
-  } else {
+  if (client_)
+    client_->OnAddObserver(obs);
+}
+
+void FakeExternalBeginFrameSource::RemoveObserver(BeginFrameObserver* obs) {
+  DCHECK(obs);
+  DCHECK(observers_.find(obs) != observers_.end());
+
+  observers_.erase(obs);
+  if (observers_.empty())
     begin_frame_task_.Cancel();
-  }
+  if (client_)
+    client_->OnRemoveObserver(obs);
 }
 
-void FakeExternalBeginFrameSource::TestOnBeginFrame() {
+void FakeExternalBeginFrameSource::TestOnBeginFrame(
+    const BeginFrameArgs& args) {
   DCHECK(CalledOnValidThread());
-  CallOnBeginFrame(CreateBeginFrameArgsForTesting(BEGINFRAME_FROM_HERE));
-  PostTestOnBeginFrame();
+  std::set<BeginFrameObserver*> observers(observers_);
+  for (auto* obs : observers)
+    obs->OnBeginFrame(args);
+  if (tick_automatically_)
+    PostTestOnBeginFrame();
 }
 
 void FakeExternalBeginFrameSource::PostTestOnBeginFrame() {
@@ -43,7 +73,9 @@ void FakeExternalBeginFrameSource::PostTestOnBeginFrame() {
       base::Bind(&FakeExternalBeginFrameSource::TestOnBeginFrame,
                  weak_ptr_factory_.GetWeakPtr()));
   base::ThreadTaskRunnerHandle::Get()->PostDelayedTask(
-      FROM_HERE, begin_frame_task_.callback(),
+      FROM_HERE,
+      base::Bind(begin_frame_task_.callback(),
+                 CreateBeginFrameArgsForTesting(BEGINFRAME_FROM_HERE)),
       base::TimeDelta::FromMilliseconds(milliseconds_per_frame_));
 }