Add support to delay sending SwapbufferAck as needed.

content/common/gpu/image_transport_surface.cc

Index: content/common/gpu/image_transport_surface.cc
diff --git a/content/common/gpu/image_transport_surface.cc b/content/common/gpu/image_transport_surface.cc
index f4c5a68cb218b02b354c2612ec7f3b18b4e89b63..8d2747c8952a4e6385722f52bf1711574bf79212 100644
--- a/content/common/gpu/image_transport_surface.cc
+++ b/content/common/gpu/image_transport_surface.cc
@@ -213,21 +213,20 @@ bool PassThroughImageTransportSurface::SwapBuffers() {
   // GetVsyncValues before SwapBuffers to work around Mali driver bug:
   // crbug.com/223558.
   SendVSyncUpdateIfAvailable();
-  bool result = gfx::GLSurfaceAdapter::SwapBuffers();
-  for (size_t i = 0; i < latency_info_.size(); i++) {
-    latency_info_[i].AddLatencyNumber(
-        ui::INPUT_EVENT_LATENCY_TERMINATED_FRAME_SWAP_COMPONENT, 0, 0);
-  }
-
-  helper_->SwapBuffersCompleted(latency_info_);
-  latency_info_.clear();
-  return result;
+  return gfx::GLSurfaceAdapter::SwapBuffersAsync(
+      base::Bind(&PassThroughImageTransportSurface::SwapBuffersCallBack,
+          base::Unretained(this)));

[piman, 2014/12/19 04:10:36]

Why is Unretained safe? Can you add a comment?

[kalyank, 2014/12/19 08:43:03]

Weakptr has a requirement that the callback be posted on same sequenced thread
and with Unretained it's Manual life time management. After a second thought,
Weakptr  looks a better choice with an added restriction here that the callback
needs to be run in Gpu main thread ?

[piman, 2014/12/19 20:32:54]

Right, that's a strong requirement. It wouldn't be ok to call
PassThroughImageTransportSurface::SwapBuffersCallBack on an arbitrary thread.

Weakptr is fine. Unretained is possible if we can ensure that the lifetime of
|this| outlives the callback - i.e. all implementations of GLSurface need to be
able to guarantee that.

 }
 
 bool PassThroughImageTransportSurface::PostSubBuffer(
     int x, int y, int width, int height) {
   SendVSyncUpdateIfAvailable();
-  bool result = gfx::GLSurfaceAdapter::PostSubBuffer(x, y, width, height);
+  return gfx::GLSurfaceAdapter::PostSubBufferAsync(x, y, width, height,
+      base::Bind(&PassThroughImageTransportSurface::SwapBuffersCallBack,
+          base::Unretained(this)));

[piman, 2014/12/19 04:10:36]

same thing here wrt Unretained.

+}
+
+void PassThroughImageTransportSurface::SwapBuffersCallBack() {
   for (size_t i = 0; i < latency_info_.size(); i++) {
     latency_info_[i].AddLatencyNumber(
         ui::INPUT_EVENT_LATENCY_TERMINATED_FRAME_SWAP_COMPONENT, 0, 0);
@@ -235,7 +234,6 @@ bool PassThroughImageTransportSurface::PostSubBuffer(
 
   helper_->SwapBuffersCompleted(latency_info_);
   latency_info_.clear();
-  return result;
 }
 
 bool PassThroughImageTransportSurface::OnMakeCurrent(gfx::GLContext* context) {