[cc] Track observer status in ExternalBeginFrameSource.

cc/scheduler/scheduler.cc

 // Copyright 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/scheduler/scheduler.h"
 
 #include <algorithm>
 
 #include "base/auto_reset.h"
 #include "base/logging.h"
@@ skipping 243 matching lines @@
 // BeginFrame is the mechanism that tells us that now is a good time to start
 // making a frame. Usually this means that user input for the frame is complete.
 // If the scheduler is busy, we queue the BeginFrame to be handled later as
 // a BeginRetroFrame.
 bool Scheduler::OnBeginFrameDerivedImpl(const BeginFrameArgs& args) {
   TRACE_EVENT1("cc,benchmark", "Scheduler::BeginFrame", "args", args.AsValue());
 
   if (!state_machine_.BeginFrameNeeded()) {
     TRACE_EVENT_INSTANT0("cc", "Scheduler::BeginFrameDropped",
                          TRACE_EVENT_SCOPE_THREAD);
+    // TODO(eseckler): Determine and set correct |ack.latest_confirmed_frame|.
+    BeginFrameAck ack(args.source_id, args.sequence_number,
+                      args.sequence_number, 0, false);
+    begin_frame_source_->DidFinishFrame(this, ack);
     return false;
   }
 
   // Trace this begin frame time through the Chrome stack
   TRACE_EVENT_FLOW_BEGIN0(
       TRACE_DISABLED_BY_DEFAULT("cc.debug.scheduler.frames"), "BeginFrameArgs",
       args.frame_time.ToInternalValue());
 
   if (settings_.using_synchronous_renderer_compositor) {
     BeginImplFrameSynchronous(args);
@@ skipping 493 matching lines @@
 }
 
 bool Scheduler::IsBeginMainFrameSentOrStarted() const {
   return (state_machine_.begin_main_frame_state() ==
               SchedulerStateMachine::BEGIN_MAIN_FRAME_STATE_SENT ||
           state_machine_.begin_main_frame_state() ==
               SchedulerStateMachine::BEGIN_MAIN_FRAME_STATE_STARTED);
 }
 
 }  // namespace cc