Switching to base::Optional<CompositorFrame> in Android's synchronous compositor IPC messages

content/browser/android/synchronous_compositor_host.cc

Index: content/browser/android/synchronous_compositor_host.cc
diff --git a/content/browser/android/synchronous_compositor_host.cc b/content/browser/android/synchronous_compositor_host.cc
index eb5a90fa6d0287d38f18ce369f439becf52ab5f9..93a79061610194c9acce049ec518719772ea3694 100644
--- a/content/browser/android/synchronous_compositor_host.cc
+++ b/content/browser/android/synchronous_compositor_host.cc
@@ -121,19 +121,20 @@ SynchronousCompositor::Frame SynchronousCompositorHost::DemandDrawHw(
                                           viewport_rect_for_tile_priority,
                                           transform_for_tile_priority);
   uint32_t compositor_frame_sink_id;
-  cc::CompositorFrame compositor_frame;
+  base::Optional<cc::CompositorFrame> compositor_frame;
   SyncCompositorCommonRendererParams common_renderer_params;
 
   if (!sender_->Send(new SyncCompositorMsg_DemandDrawHw(
           routing_id_, params, &common_renderer_params,
-          &compositor_frame_sink_id, &compositor_frame))) {
+          &compositor_frame_sink_id, &compositor_frame)) ||
+      !compositor_frame) {

[boliu, 2016/10/27 19:52:15]

not quite the same. ProcessHardwareFrame can be skipped, but ProcessCommonParams
shouldn't be dropped if the frame is empty

     return SynchronousCompositor::Frame();
   }
 
   ProcessCommonParams(common_renderer_params);
 
   return ProcessHardwareFrame(compositor_frame_sink_id,
-                              std::move(compositor_frame));
+                              std::move(*compositor_frame));
 }
 
 SynchronousCompositor::Frame SynchronousCompositorHost::ProcessHardwareFrame(
@@ -143,13 +144,7 @@ SynchronousCompositor::Frame SynchronousCompositorHost::ProcessHardwareFrame(
   frame.frame.reset(new cc::CompositorFrame);
   frame.compositor_frame_sink_id = compositor_frame_sink_id;
   *frame.frame = std::move(compositor_frame);
-  if (!frame.frame->delegated_frame_data) {
-    // This can happen if compositor did not swap in this draw.
-    frame.frame.reset();
-  }
-  if (frame.frame) {
-    UpdateFrameMetaData(frame.frame->metadata.Clone());
-  }
+  UpdateFrameMetaData(frame.frame->metadata.Clone());
   return frame;
 }