cc: Introduce embedded_surfaces in metadata for surface Ids in draw quads

cc/output/compositor_frame_metadata.h

 // Copyright (c) 2012 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.
 
 #ifndef CC_OUTPUT_COMPOSITOR_FRAME_METADATA_H_
 #define CC_OUTPUT_COMPOSITOR_FRAME_METADATA_H_
 
 #include <stdint.h>
 
 #include <vector>
@@ skipping 59 matching lines @@
   // it's too small to fill the box the parent reserved for it.
   SkColor root_background_color = SK_ColorWHITE;
 
   // Provides selection region updates relative to the current viewport. If the
   // selection is empty or otherwise unused, the bound types will indicate such.
   Selection<gfx::SelectionBound> selection;
 
   std::vector<ui::LatencyInfo> latency_info;
 
   // This is the set of Surfaces that are referenced by this frame.
+  // Note: this includes occluded and clipped surfaces and surfaces that may
+  // be accessed by this CompositorFrame in the future.
+  // TODO(fsamuel): In the future, a generalized frame eviction system will
+  // determine which surfaces to retain and which to evict. It will likely
+  // be unnecessary for the embedder to explicitly specify which surfaces to
+  // retain. Thus, this field will likely go away.
   std::vector<SurfaceId> referenced_surfaces;
 
+  // This is the set of SurfaceIds embedded in DrawQuads.
+  std::vector<SurfaceId> embedded_surfaces;
+
   // This indicates whether this CompositorFrame can be activated before
   // dependencies have been resolved.
   bool can_activate_before_dependencies = true;
 
   // This is a value that allows the browser to associate compositor frames
   // with the content that they represent -- typically top-level page loads.
   // TODO(kenrb, fsamuel): This should eventually by SurfaceID, when they
   // become available in all renderer processes. See https://crbug.com/695579.
   uint32_t content_source_id = 0;
 
   // BeginFrameAck for the BeginFrame that this CompositorFrame answers.
   BeginFrameAck begin_frame_ack;
 
   // Once the display compositor processes a frame containing a non-zero frame
   // token, the token is sent to embedder of the frame. This is helpful when
   // the embedder wants to do something after a particular frame is processed.
   uint32_t frame_token = 0;
 
  private:
   CompositorFrameMetadata(const CompositorFrameMetadata& other);
   CompositorFrameMetadata operator=(const CompositorFrameMetadata&) = delete;
 };
 
 }  // namespace cc
 
 #endif  // CC_OUTPUT_COMPOSITOR_FRAME_METADATA_H_