sync compositor: Send ipc reply in swap

content/browser/android/in_process/synchronous_compositor_impl.cc

Index: content/browser/android/in_process/synchronous_compositor_impl.cc
diff --git a/content/browser/android/in_process/synchronous_compositor_impl.cc b/content/browser/android/in_process/synchronous_compositor_impl.cc
index 4d64521a57bde82141caef4440af9e771d808c81..e5c789b7b09686c7b16c3d1c6103aa883a803e65 100644
--- a/content/browser/android/in_process/synchronous_compositor_impl.cc
+++ b/content/browser/android/in_process/synchronous_compositor_impl.cc
@@ -4,6 +4,8 @@
 
 #include "content/browser/android/in_process/synchronous_compositor_impl.h"
 
+#include <utility>
+
 #include "base/auto_reset.h"
 #include "base/bind.h"
 #include "base/lazy_instance.h"
@@ -163,19 +165,16 @@ scoped_ptr<cc::CompositorFrame> SynchronousCompositorImpl::DemandDrawHw(
   DCHECK(CalledOnValidThread());
   DCHECK(output_surface_);
   DCHECK(begin_frame_source_);
+  DCHECK(!frame_holder_);
 
-  scoped_ptr<cc::CompositorFrame> frame =
-      output_surface_->DemandDrawHw(surface_size,
-                                    transform,
-                                    viewport,
-                                    clip,
-                                    viewport_rect_for_tile_priority,
-                                    transform_for_tile_priority);
+  output_surface_->DemandDrawHw(surface_size, transform, viewport, clip,
+                                viewport_rect_for_tile_priority,
+                                transform_for_tile_priority);
 
-  if (frame.get())
-    UpdateFrameMetaData(frame->metadata);
+  if (frame_holder_)

[hush (inactive), 2015/12/29 19:42:17]

just checking, because the DemandDrawHw is synchronous here, doing so with the
in process compositor has no performance benefit right? This is done for the
sake of consistency with CompositorProxy implementation.

[boliu, 2015/12/29 20:22:52]

Yep. SynchronousCompositorOutputSurface implementation is shared between
in-process and ipc paths.

+    UpdateFrameMetaData(frame_holder_->metadata);
 
-  return frame.Pass();
+  return std::move(frame_holder_);

[hush (inactive), 2015/12/29 19:42:17]

How is this is different from frame_holder_.pass()? No difference?

[boliu, 2015/12/29 20:22:52]

No difference afaik. Presumit check says std::move is the way to go now.

Note that for scoped_ptr (and std::unique_ptr), the moved-from value after move
is defined to be null (just like Pass), so no need to null it out afterwards.
This is not true for types in general; apparently specs says the moved-from
value becomes undefined, and only safe operations on it after move are
assignment and destruction.

 }
 
 void SynchronousCompositorImpl::ReturnResources(
@@ -188,14 +187,23 @@ bool SynchronousCompositorImpl::DemandDrawSw(SkCanvas* canvas) {
   DCHECK(CalledOnValidThread());
   DCHECK(output_surface_);
   DCHECK(begin_frame_source_);
+  DCHECK(!frame_holder_);
+
+  output_surface_->DemandDrawSw(canvas);
 
-  scoped_ptr<cc::CompositorFrame> frame =
-      output_surface_->DemandDrawSw(canvas);
+  bool success = !!frame_holder_;
+  if (frame_holder_) {
+    UpdateFrameMetaData(frame_holder_->metadata);
+    frame_holder_.reset();
+  }
 
-  if (frame.get())
-    UpdateFrameMetaData(frame->metadata);
+  return success;
+}
 
-  return !!frame.get();
+void SynchronousCompositorImpl::SwapBuffers(cc::CompositorFrame* frame) {
+  DCHECK(!frame_holder_);
+  frame_holder_.reset(new cc::CompositorFrame);
+  frame->AssignTo(frame_holder_.get());
 }
 
 void SynchronousCompositorImpl::UpdateFrameMetaData(