cc: Unify use of DidSwapBuffers() and did_request_swap

cc/scheduler/scheduler.cc

Index: cc/scheduler/scheduler.cc
diff --git a/cc/scheduler/scheduler.cc b/cc/scheduler/scheduler.cc
index 88c8c74f701d2f4aa0a8980cff8b01f2a21335ea..c49dc803a26feb3209447a8c782849adb365b844 100644
--- a/cc/scheduler/scheduler.cc
+++ b/cc/scheduler/scheduler.cc
@@ -191,6 +191,10 @@ void Scheduler::SetMaxSwapsPending(int max) {
 
 void Scheduler::DidSwapBuffers() {
   state_machine_.DidSwapBuffers();
+
+  // Swap should not occur inside readback operation.
+  DCHECK(!IsInsideAction(SchedulerStateMachine::ACTION_DRAW_AND_READBACK));
+
   // There is no need to call ProcessScheduledActions here because
   // swapping should not trigger any new actions.
   if (!inside_process_scheduled_actions_) {
@@ -601,18 +605,8 @@ bool Scheduler::IsBeginMainFrameSent() const {
 }
 
 void Scheduler::DrawAndSwapIfPossible() {
-  DrawSwapReadbackResult result =
-      client_->ScheduledActionDrawAndSwapIfPossible();
-  state_machine_.DidDrawIfPossibleCompleted(result.draw_result);
-}
-
-void Scheduler::DrawAndSwapForced() {
-  client_->ScheduledActionDrawAndSwapForced();
-}
-
-void Scheduler::DrawAndReadback() {
-  DrawSwapReadbackResult result = client_->ScheduledActionDrawAndReadback();
-  DCHECK(!result.did_request_swap);
+  DrawResult result = client_->ScheduledActionDrawAndSwapIfPossible();
+  state_machine_.DidDrawIfPossibleCompleted(result);
 }
 
 void Scheduler::ProcessScheduledActions() {
@@ -656,14 +650,14 @@ void Scheduler::ProcessScheduledActions() {
         DrawAndSwapIfPossible();
         break;
       case SchedulerStateMachine::ACTION_DRAW_AND_SWAP_FORCED:
-        DrawAndSwapForced();
+        client_->ScheduledActionDrawAndSwapForced();
         break;
       case SchedulerStateMachine::ACTION_DRAW_AND_SWAP_ABORT:
         // No action is actually performed, but this allows the state machine to
         // advance out of its waiting to draw state without actually drawing.
         break;
       case SchedulerStateMachine::ACTION_DRAW_AND_READBACK:
-        DrawAndReadback();
+        client_->ScheduledActionDrawAndReadback();
         break;
       case SchedulerStateMachine::ACTION_BEGIN_OUTPUT_SURFACE_CREATION:
         client_->ScheduledActionBeginOutputSurfaceCreation();