Do not send a frame swap ack from the browser until the frame is drawn

content/browser/renderer_host/render_widget_host_impl.cc

Index: content/browser/renderer_host/render_widget_host_impl.cc
diff --git a/content/browser/renderer_host/render_widget_host_impl.cc b/content/browser/renderer_host/render_widget_host_impl.cc
index df2e948b3b5f88f012eba529579ded3e71a8c202..17cc7263bcf6b121b7b624e05164af9dd23689b8 100644
--- a/content/browser/renderer_host/render_widget_host_impl.cc
+++ b/content/browser/renderer_host/render_widget_host_impl.cc
@@ -787,6 +787,12 @@ void RenderWidgetHostImpl::PaintAtSize(TransportDIB::Handle dib_handle,
                                page_size, desired_size));
 }
 
+void RenderWidgetHostImpl::SetAboutToWaitForBackingStoreCallback(
+    const base::Closure& about_to_wait_for_backing_store_callback) {
+  about_to_wait_for_backing_store_callback_ =
+      about_to_wait_for_backing_store_callback;
+}
+
 bool RenderWidgetHostImpl::TryGetBackingStore(const gfx::Size& desired_size,
                                               BackingStore** backing_store) {
   // Check if the view has an accelerated surface of the desired size.
@@ -856,6 +862,11 @@ BackingStore* RenderWidgetHostImpl::GetBackingStore(bool force_create) {
   do {
     TRACE_EVENT0("renderer_host", "GetBackingStore::WaitForUpdate");
 
+    // Release any backpressure preventing the renderer from generating new
+    // frames.
+    if (!about_to_wait_for_backing_store_callback_.is_null())
+      about_to_wait_for_backing_store_callback_.Run();

[ccameron, 2014/02/14 02:19:06]

The call that we need it before is this guy. It's a loop that pumps the renderer
for frames until it gets one of the right size.

[piman, 2014/02/14 02:59:02]

RWHVMac could send the ack right away when receiving the
AcceleratedBuffersSwapped if it's the wrong size?

You'd wrap the calls to GetBackingStore(true) by something like

BackingStoreMac* RWHVMac::GetBackingStoreSync() {
  waiting_for_backing_store_ = true;
  SendPendingAcks();
  BackingStoreMac* bs = rwh->GetBackingStore(true);
  waiting_for_backing_store_ = false;
  return bs;
}

Then in RWHVMac::AcceleratedSurfaceBuffersSwapped() {
  // [...]
  AddPendingSwapAck();     
  if (size != expected_size && waiting_for_backing_store_) {
    SendPendingAcks();
    return;
  }
}

That even lets you skip a bunch of the logic that you don't care about since
it's not a frame of the right size.

We do something essentially similar in RWHVAura, minus the "block the main
thread" part (instead we prevent the compositor from drawing). See the
RenderWidgetHostViewAura::ShouldSkipFrame and callers.

+
     // When we have asked the RenderWidget to resize, and we are still waiting
     // on a response, block for a little while to see if we can't get a response
     // before returning the old (incorrectly sized) backing store.