Added MojoCompositorFrameSink::EvictFrame() and MojoCompositorFrameSinkClient::WillDrawSurface()

cc/ipc/mojo_compositor_frame_sink.mojom

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 module cc.mojom;
 
 import "cc/ipc/begin_frame_args.mojom";
 import "cc/ipc/compositor_frame.mojom";
 import "cc/ipc/frame_sink_id.mojom";
 import "cc/ipc/local_frame_id.mojom";
@@ skipping 13 matching lines @@
   // to screen the next time frames from all CompositorFrameSinks are aggregated
   // to produce a display CompositorFrame. If a client wishes to allocate a new
   // surface (e.g. during resize), then it can simply allocate a new
   // |local_frame_id|.
   // For successful swaps, the implementation must call
   // DidReceiveCompositorFrameAck() asynchronously when the frame has been
   // processed in order to unthrottle the next frame.
   SubmitCompositorFrame(cc.mojom.LocalFrameId local_frame_id,
                         cc.mojom.CompositorFrame frame);
 
+  // Notify that the surface is no longer in use (and is okay to be evicted) so
+  // that its resources gets returned in time.
+  EvictFrame();
+
   // TODO(fsamuel): ReadbackBitmap API would be useful here.
 };
 
 interface MojoCompositorFrameSinkClient {
   // Notification that the previous CompositorFrame given to
   // SubmitCompositorFrame() has been processed and that another frame
   // can be submitted. This provides backpressure from the display compositor
   // so that frames are submitted only at the rate it can handle them.
   // TODO(fsamuel): This method ought not be necessary with unified BeginFrame.
   // However, there's a fair amount of cleanup and refactoring necessary to get
   // rid of it.
   DidReceiveCompositorFrameAck();
 
   // Notification for the client to generate a CompositorFrame.
   OnBeginFrame(BeginFrameArgs args);
 
   // Returns resources sent to SubmitCompositorFrame to be reused or freed.
   ReclaimResources(ReturnedResourceArray resources);
+
+  // Called when surface is being scheduled for a draw.
+  WillDrawSurface();

[danakj, 2016/12/02 00:01:14]

no damage rect or local frame id?

[Alex Z., 2016/12/02 16:17:15]

This was first added in https://codereview.chromium.org/2493223002/ for
exo::Surface.
Local frame ID was not needed because exo::Surface manages its own damage rect
and local frame ID. 
exo::Surface doesn't need a damage rect for its own WillDraw().

MojoCompositorFrameSink::SubmitCompositorFrame() now takes a LocalFrameId so I
think it should be fine.

 };
 
 // MojoCompositorFrameSinkPrivate is used by the display compositor host to set
 // up BeginFrameSource hierarchies.  This API lives in SurfaceManager but is
 // called from here in order to ensure that hierarchy registration does not race
 // CompositorFrameSink creation.
 interface MojoCompositorFrameSinkPrivate {
   AddChildFrameSink(FrameSinkId child_frame_sink_id);
   RemoveChildFrameSink(FrameSinkId child_frame_sink_id);
 };