cc: Fix negative EstimatedParentDrawTimes

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/debug/trace_event.h"
 #include "base/logging.h"
@@ skipping 119 matching lines @@
                                       base::TimeDelta interval) {
   // TODO(brianderson): We should not be receiving 0 intervals.
   if (interval == base::TimeDelta())
     interval = BeginFrameArgs::DefaultInterval();
   vsync_interval_ = interval;
   if (!settings_.begin_frame_scheduling_enabled)
     synthetic_begin_frame_source_->CommitVSyncParameters(timebase, interval);
 }
 
 void Scheduler::SetEstimatedParentDrawTime(base::TimeDelta draw_time) {
+  DCHECK_GE(draw_time.ToInternalValue(), 0);
   estimated_parent_draw_time_ = draw_time;
 }
 
 void Scheduler::SetCanStart() {
   state_machine_.SetCanStart();
   ProcessScheduledActions();
 }
 
 void Scheduler::SetVisible(bool visible) {
   state_machine_.SetVisible(visible);
@@ skipping 587 matching lines @@
 }
 
 bool Scheduler::IsBeginMainFrameSentOrStarted() const {
   return (state_machine_.commit_state() ==
               SchedulerStateMachine::COMMIT_STATE_BEGIN_MAIN_FRAME_SENT ||
           state_machine_.commit_state() ==
               SchedulerStateMachine::COMMIT_STATE_BEGIN_MAIN_FRAME_STARTED);
 }
 
 }  // namespace cc