[blimp] Add SkPicture caching support.

cc/blimp/engine_picture_cache.h

+// 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.
+
+#ifndef CC_BLIMP_ENGINE_PICTURE_CACHE_H_
+#define CC_BLIMP_ENGINE_PICTURE_CACHE_H_
+
+#include <vector>
+
+class SkPicture;
+
+namespace cc {
+struct PictureData;
+
+// EnginePictureCache provides functionaltiy for marking when SkPictures are in
+// use an when they stop being in use. Based on this, a PictureCacheUpdate can
+// be retrieved that includes all the new items since last time it was called.
+// This PictureCacheUpdate is then supposed to be sent to the client.
+class EnginePictureCache {
+ public:
+  virtual ~EnginePictureCache() {}
+
+  // MarkUsed must be called when an SkPicture needs to available on the client.
+  virtual void MarkUsed(const SkPicture* picture) = 0;
+
+  // Called when a PictureCacheUpdate is going to be sent to the client. This
+  // must contain all the new SkPictures that are in use since last call.
+  virtual std::vector<PictureData> CalculateCacheUpdateAndFlush() = 0;
+};
+
+}  // namespace cc
+
+#endif  // CC_BLIMP_ENGINE_PICTURE_CACHE_H_