[blimp] Add SkPicture caching support.

cc/proto/display_item.proto

 // Copyright 2015 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.
 
 syntax = "proto2";
 
 import "skregion.proto";
 import "skrrect.proto";
 import "skxfermode.proto";
 import "rect.proto";
@@ skipping 56 matching lines @@
 }
 
 message CompositingDisplayItem {
   optional uint32 alpha = 1;
   optional cc.proto.SkXfermode.Mode mode = 2;
   optional cc.proto.RectF bounds = 3;
   optional bytes color_filter = 4; /* SkColorFilter */
   optional bool lcd_text_requires_opaque_layer = 5;
 }
 
+message SkPictureID {
+  optional uint32 unique_id = 1;
+}
+
 message DrawingDisplayItem {
-  optional bytes picture = 1; /* SkPicture */
+  optional SkPictureID id = 1;
 }
 
 message FilterDisplayItem {
   optional cc.proto.RectF bounds = 1;
 
   // TODO(dtrainor): Support FilterOperations.
 }
 
 message FloatClipDisplayItem {
   optional cc.proto.RectF clip_rect = 1;
 }
 
 message TransformDisplayItem {
   optional cc.proto.Transform transform = 1;
 }