Make skia.mojom.Bitmap use shared buffer

skia/public/interfaces/bitmap.mojom

Index: skia/public/interfaces/bitmap.mojom
diff --git a/skia/public/interfaces/bitmap.mojom b/skia/public/interfaces/bitmap.mojom
index b02833af03fc8792aea533f8655f07544fa748e9..f3aae5e8e1ef5e898207af03a29af773c38ef5e5 100644
--- a/skia/public/interfaces/bitmap.mojom
+++ b/skia/public/interfaces/bitmap.mojom
@@ -41,5 +41,6 @@ struct Bitmap {
   uint32 height;
   uint64 row_bytes;
 
-  array<uint8> pixel_data;
+  // Handle could be null if the bitmap is empty.
+  handle<shared_buffer>? pixel_data_buffer_handle;

[msw, 2017/03/25 00:59:52]

Does it make sense to have our only SkBitmap transport work via shared memory?
Don't we then need to guarantee that all users keep their SkBitmaps alive for
the unknown duration needed by the remote mojom impl?

[Ken Rockot(use gerrit already), 2017/03/26 17:52:50]

No, the shared buffer is allocated during serialization and will remain alive as
long as there are any handles referencing it. The bitmap data is copied into the
buffer at that point, and the handle sent to the receiver is enough to keep the
buffer alive.

 };