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

content/browser/android/synchronous_compositor_host.cc

 // Copyright 2015 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/android/synchronous_compositor_host.h"
 
 #include <utility>
 
 #include "base/command_line.h"
 #include "base/containers/hash_tables.h"
@@ skipping 103 matching lines @@
 }
 
 SynchronousCompositor::Frame SynchronousCompositorHost::DemandDrawHw(
     const gfx::Size& viewport_size,
     const gfx::Rect& viewport_rect_for_tile_priority,
     const gfx::Transform& transform_for_tile_priority) {
   SyncCompositorDemandDrawHwParams params(viewport_size,
                                           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(
     uint32_t compositor_frame_sink_id,
     cc::CompositorFrame compositor_frame) {
   SynchronousCompositor::Frame frame;
   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;
 }
 
 void SynchronousCompositorHost::UpdateFrameMetaData(
     cc::CompositorFrameMetadata frame_metadata) {
   rwhva_->SynchronousFrameMetadata(std::move(frame_metadata));
 }
 
 SynchronousCompositorBrowserFilter* SynchronousCompositorHost::GetFilter() {
   return static_cast<RenderProcessHostImpl*>(
@@ skipping 252 matching lines @@
   if (params.page_scale_factor) {
     client_->UpdateRootLayerState(
         this, gfx::ScrollOffsetToVector2dF(params.total_scroll_offset),
         gfx::ScrollOffsetToVector2dF(params.max_scroll_offset),
         params.scrollable_size, params.page_scale_factor,
         params.min_page_scale_factor, params.max_page_scale_factor);
   }
 }
 
 }  // namespace content