MojoCompositorFrameSinkPrivate should support copy requests

cc/ipc/mojo_compositor_frame_sink.mojom

Index: cc/ipc/mojo_compositor_frame_sink.mojom
diff --git a/cc/ipc/mojo_compositor_frame_sink.mojom b/cc/ipc/mojo_compositor_frame_sink.mojom
index bf2e196f79956523a6f3e578a2decc796cd35959..1826ca8a2da795e89d962a782ed6c2bce4d35daa 100644
--- a/cc/ipc/mojo_compositor_frame_sink.mojom
+++ b/cc/ipc/mojo_compositor_frame_sink.mojom
@@ -6,11 +6,15 @@ module cc.mojom;
 
 import "cc/ipc/begin_frame_args.mojom";
 import "cc/ipc/compositor_frame.mojom";
+import "cc/ipc/copy_output_request.mojom";
+import "cc/ipc/copy_output_result.mojom";
 import "cc/ipc/frame_sink_id.mojom";
 import "cc/ipc/local_surface_id.mojom";
 import "cc/ipc/surface_reference.mojom";
 import "cc/ipc/returned_resource.mojom";
 import "cc/ipc/surface_sequence.mojom";
+import "gpu/ipc/common/mailbox.mojom";
+import "gpu/ipc/common/sync_token.mojom";
 
 // A MojoCompositorFrameSink is an interface for receiving CompositorFrame
 // structs. A CompositorFrame contains the complete output meant for display.
@@ -46,8 +50,6 @@ interface MojoCompositorFrameSink {
 
   // Mark the sequence as satisfied and garbage collect surfaces.
   Satisfy(cc.mojom.SurfaceSequence sequence);
-
-  // TODO(fsamuel): ReadbackBitmap API would be useful here.
 };
 
 interface MojoCompositorFrameSinkClient {
@@ -77,4 +79,15 @@ interface MojoCompositorFrameSinkClient {
 interface MojoCompositorFrameSinkPrivate {
   AddChildFrameSink(FrameSinkId child_frame_sink_id);
   RemoveChildFrameSink(FrameSinkId child_frame_sink_id);
+
+  // Requests that the renderer send back a copy of the surface that this
+  // CompositorFrameSink submits to. The result can be in form of a bitmap
+  // or a texture. See cc::CopyOutputRequest and cc::CopyOutputResult.
+  RequestCopyOfSurface(cc.mojom.CopyOutputRequest request)
+      => (cc.mojom.CopyOutputResult result);
+
+  // If the copy returned by RequestCopyOfSurface is a texture, this method

[danakj, 2017/02/06 23:02:12]

This might be off-topic but what if it's a bitmap, do we use shared memory or do
we now ship a lot of pixels over ipc? What does
https://cs.chromium.org/chromium/src/cc/ipc/copy_output_result.mojom?rcl=5fdb...
do? Should that be a SharedBitmap?

[Saman Sami, 2017/02/06 23:09:54]

We serialize the bitmap and send it over IPC. I'm not sure how to use shared
bitmap. CopyOutputResult only has a SkBitmap. That might need to change I guess?

[danakj, 2017/02/06 23:24:07]

Yeh it would have to. We should do that cuz copying pixels is slow.

[Saman Sami, 2017/02/13 23:07:37]

I agree. I created a new bug to track this issue. https://crbug.com/691070

+  // must be used to release it.
+  ReleaseCopyOfSurface(gpu.mojom.Mailbox mailbox,
+                       gpu.mojom.SyncToken sync_token, bool is_lost);
 };