Mac ÜC: Enable GPU back-pressure from the browser to the renderer

content/browser/compositor/delegated_frame_host.cc

 // Copyright 2014 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 "content/browser/compositor/delegated_frame_host.h"
 
 #include "base/callback_helpers.h"
 #include "base/command_line.h"
 #include "cc/output/compositor_frame.h"
 #include "cc/output/compositor_frame_ack.h"
@@ skipping 733 matching lines @@
     // We may have had a resize while we had the lock (e.g. if the lock expired,
     // or if the UI still gave us some resizes), so make sure we grab a new lock
     // if necessary.
     MaybeCreateResizeLock();
   }
 }
 
 void DelegatedFrameHost::OnCompositingStarted(
     ui::Compositor* compositor, base::TimeTicks start_time) {
   last_draw_ended_ = start_time;
+  client_->DelegatedCompositorDidSwapBuffers();

[ccameron, 2014/06/05 01:31:52]

This is called from SingleThreadProxy::DidSwapFrame, which then gets renamed to
DidCommitAndDrawFrame, then to OnCompositingStarted, completely obscuring what's
actually happening here.

Also, there is a bug in SingleThreadProxy::DidSwapFrame which makes this
sometimes get called when there is no frame (I'm addressing that in a separate
CL, with unit tests, etc, to make sure it doesn't happen again).

 }
 
 void DelegatedFrameHost::OnCompositingEnded(
     ui::Compositor* compositor) {
 }
 
-void DelegatedFrameHost::OnCompositingAborted(
-    ui::Compositor* compositor) {
+void DelegatedFrameHost::OnCompositingAborted(ui::Compositor* compositor) {
+  client_->DelegatedCompositorAbortedSwapBuffers();
 }
 
 void DelegatedFrameHost::OnCompositingLockStateChanged(
     ui::Compositor* compositor) {
   // A compositor lock that is part of a resize lock timed out. We
   // should display a renderer frame.
   if (!compositor->IsLocked() && can_lock_compositor_ == YES_DID_LOCK) {
     can_lock_compositor_ = NO_PENDING_RENDERER_FRAME;
   }
 }
@@ skipping 103 matching lines @@
   // that should keep our frame. old_layer will be returned to the
   // RecreateLayer caller, and should have a copy.
   if (frame_provider_.get()) {
     new_layer->SetShowDelegatedContent(frame_provider_.get(),
                                        current_frame_size_in_dip_);
   }
 }
 
 }  // namespace content