Added FrameFuture class

content/public/browser/android/synchronous_compositor.h

Index: content/public/browser/android/synchronous_compositor.h
diff --git a/content/public/browser/android/synchronous_compositor.h b/content/public/browser/android/synchronous_compositor.h
index 5b8b72328f5d55ff681c725f1c29db00564eca41..11477d13da267a16ffdb09b8163060afd0204019 100644
--- a/content/public/browser/android/synchronous_compositor.h
+++ b/content/public/browser/android/synchronous_compositor.h
@@ -10,6 +10,7 @@
 #include <memory>
 
 #include "base/memory/ref_counted.h"
+#include "base/synchronization/waitable_event.h"
 #include "base/time/time.h"
 #include "cc/resources/returned_resource.h"
 #include "content/common/content_export.h"
@@ -59,11 +60,27 @@ class CONTENT_EXPORT SynchronousCompositor {
     DISALLOW_COPY_AND_ASSIGN(Frame);
   };
 
+  class FrameFuture : public base::RefCountedThreadSafe<FrameFuture> {
+   public:
+    FrameFuture();
+    void setFrame(std::unique_ptr<SynchronousCompositor::Frame> frame);
+    SynchronousCompositor::Frame* getFrame();
+    void Wait();

[boliu, 2016/09/20 00:27:56]

there should be no Wait or hasFrame, and getFrame should be called only once and
return unique_ptr<Frame> (no need for the SynchronousCompositor:: qualification
here)

Then add DCHECKs to make sure getFrame is only called once, as discussed

[ojars, 2016/09/22 18:21:39]

Done.

+    bool hasFrame();
+
+   private:
+    base::WaitableEvent waitable_event_;
+    std::unique_ptr<content::SynchronousCompositor::Frame> frame_;
+    friend class base::RefCountedThreadSafe<FrameFuture>;
+    ~FrameFuture();
+  };
+
   // "On demand" hardware draw. Parameters are used by compositor for this draw.
   // |viewport_size| is the current size to improve results during resize.
   // |viewport_rect_for_tile_priority| and |transform_for_tile_priority| are
   // used to customize the tiling decisions of compositor.
-  virtual Frame DemandDrawHw(
+  // TODO(ojars): update this and the next documentation
+  virtual scoped_refptr<FrameFuture> DemandDrawHw(
       const gfx::Size& viewport_size,
       const gfx::Rect& viewport_rect_for_tile_priority,
       const gfx::Transform& transform_for_tile_priority) = 0;
@@ -71,7 +88,7 @@ class CONTENT_EXPORT SynchronousCompositor {
   // Same as DemandDrawHw, but uses asynchronous IPC messages. Calls
   // SynchronousCompositorClient::OnDrawHardwareProcessFrame to return the
   // frame.
-  virtual void DemandDrawHwAsync(
+  virtual scoped_refptr<FrameFuture> DemandDrawHwAsync(
       const gfx::Size& viewport_size,
       const gfx::Rect& viewport_rect_for_tile_priority,
       const gfx::Transform& transform_for_tile_priority) = 0;