cc: modify the waiting condition of forced commit

Forced commit only should proceed to its BeginMainFrame when there is a
scheduled BeginMainFrame().
So, Forced commit only should wait for COMMIT_STATE_BEGIN_MAIN_FRAME_SENT.

R=brianderson@chromium.org
BUG=350585
TEST=cc_unittests

Review URL: https://codereview.chromium.org/189553007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@255894 0039d316-1c4b-4281-b951-d872f2087c98

cc/scheduler/scheduler.cc

@@ -294,6 +294,11 @@ void Scheduler::PollForAnticipatedDrawTriggers() {
   state_machine_.DidLeavePollForAnticipatedDrawTriggers();
 }
 
+bool Scheduler::IsBeginMainFrameSent() const {
+  return state_machine_.commit_state() ==
+         SchedulerStateMachine::COMMIT_STATE_BEGIN_MAIN_FRAME_SENT;
+}
+
 void Scheduler::DrawAndSwapIfPossible() {
   DrawSwapReadbackResult result =
       client_->ScheduledActionDrawAndSwapIfPossible();

cc/scheduler/scheduler.h

@@ -118,6 +118,8 @@ class CC_EXPORT Scheduler {
     return inside_action_ == action;
   }
 
+  bool IsBeginMainFrameSent() const;
+
  private:
   Scheduler(SchedulerClient* client,
             const SchedulerSettings& scheduler_settings,

cc/trees/thread_proxy.cc

@@ -207,7 +207,7 @@ void ThreadProxy::ForceCommitForReadbackOnImplThread(
   impl().readback_request = request;
 
   impl().scheduler->SetNeedsForcedCommitForReadback();
-  if (impl().scheduler->CommitPending()) {
+  if (impl().scheduler->IsBeginMainFrameSent()) {
     begin_main_frame_sent_completion->Signal();
     return;
   }