Pipe impl_latency_takes_priority_ to the RenderScheduler.

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 336 matching lines @@
   TRACE_EVENT1("cc,benchmark", "Scheduler::BeginFrame", "args", args.AsValue());
 
   // 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());
 
   // TODO(brianderson): Adjust deadline in the DisplayScheduler.
   BeginFrameArgs adjusted_args(args);
   adjusted_args.deadline -= EstimatedParentDrawTime();
+  adjusted_args.on_critical_path = !ImplLatencyTakesPriority();

[brianderson, 2015/06/09 01:12:42]

Depending on how the Renderer scheduler uses this flag, you may also want to
make on_critical_path false when MainThreadIsInHighLatencyMode and
!SkipNextBeginMainFrameToReduceLatency since there's no chance of running in
low-latency anyway, but that can come in a followup patch.

[Sami, 2015/06/09 09:47:34]

When this flag is false, the renderer scheduler is going to allow some
non-critical work (e.g., timers) to run with an equal priority to the
BeginFrame. In other words the semantic is that this BeginFrame isn't really
that urgent, so no rush. Do you think the combination high latency and !skip has
that same meaning?

[brianderson, 2015/06/10 01:13:35]

Hmm, probably not. It's more of an in-between priority where the main thread has
a little more time to respond than in low latency mode. A better way to
communicate might be to use a later deadline. Anyways, no need to worry about
this now.

 
   // Deliver BeginFrames to children.
   // TODO(brianderson): Move this responsibility to the DisplayScheduler.
   if (state_machine_.children_need_begin_frames())
     client_->SendBeginFramesToChildren(adjusted_args);
 
   if (settings_.using_synchronous_renderer_compositor) {
     BeginImplFrameSynchronous(adjusted_args);
     return true;
   }
@@ skipping 453 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