Add DIRECT_COMPOSITION GpuMemoryBuffer type.

ui/gfx/buffer_types.h

Index: ui/gfx/buffer_types.h
diff --git a/ui/gfx/buffer_types.h b/ui/gfx/buffer_types.h
index 179ee1941b42e828353daed7a90998d8fddd4e7e..83d13fa2d10a7496e1fc8ec63a044fb10511b6e9 100644
--- a/ui/gfx/buffer_types.h
+++ b/ui/gfx/buffer_types.h
@@ -41,6 +41,9 @@ enum class BufferFormat {
 enum class BufferUsage {
   GPU_READ,
   SCANOUT,
+  // Flips of SCANOUT_ASYNC buffers are not synchronized with flips of other
+  // buffers or overlay updates.
+  SCANOUT_ASYNC,

[reveman, 2017/06/14 21:35:59]

Why do we need to add this here? How flips are synchronized doesn't seem like
something that buffer usage should be used for..

[jbauman, 2017/06/14 22:18:17]

I wasn't sure how to specify the type of buffer needed (IDCompositionSurface or
IDXGISwapChain) to GpuMemoryBufferManager::CreateGpuMemoryBuffer. Would you want
me to add an extra argument to that?

   SCANOUT_CPU_READ_WRITE,
   GPU_READ_CPU_READ_WRITE,
   // TODO(reveman): Merge this with GPU_READ_CPU_READ_WRITE when SurfaceTexture