[blimp] Add SkPicture caching support.

blimp/common/compositor/blimp_picture_cache_registry.h

Index: blimp/common/compositor/blimp_picture_cache_registry.h
diff --git a/blimp/common/compositor/blimp_picture_cache_registry.h b/blimp/common/compositor/blimp_picture_cache_registry.h
new file mode 100644
index 0000000000000000000000000000000000000000..64eaaa1cd05c1fa8885a74f0e6fdebfd9c22e11a
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+++ b/blimp/common/compositor/blimp_picture_cache_registry.h
@@ -0,0 +1,56 @@
+// 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 BLIMP_COMMON_COMPOSITOR_BLIMP_PICTURE_CACHE_REGISTRY_H_
+#define BLIMP_COMMON_COMPOSITOR_BLIMP_PICTURE_CACHE_REGISTRY_H_
+
+#include <stdint.h>
+#include <map>
+#include <set>
+
+#include "base/macros.h"
+#include "blimp/common/blimp_common_export.h"
+
+namespace blimp {
+
+// BlimpPictureCacheRegistry provides functionality to count the number of
+// references to a given item. Items can be staged an unstaged which in practice
+// increments and decrements their reference count, respectively.
+// When all items have been staged, the Commit() functions provides the deltas
+// since last call to Commit(), as sets of added and removed entries.
+// It is not necessary to stage an item if it has already been committed. Only
+// changes to the reference count need to be informed.
+// It is illegal to have a negative reference count.
+class BLIMP_COMMON_EXPORT BlimpPictureCacheRegistry {
+ public:
+  BlimpPictureCacheRegistry();
+  ~BlimpPictureCacheRegistry();
+
+  // Stage an item for commit. This increments the reference count for the
+  // given |item|. Must be called before Unstage of that item.
+  void Stage(uint32_t item);
+
+  // Unstage an item for commit. This decrements the reference count for the
+  // given |item|.
+  void Unstage(uint32_t item);
+
+  // Calculates the delta since last call to Commit() and provides the result
+  // in the output params |added_items| and |removed_items|.
+  void Commit(std::set<uint32_t>* added_items,
+              std::set<uint32_t>* removed_items);
+
+ private:
+  // A reference count for all the given items. The key is the item, and the
+  // value is the count for that item.
+  std::map<uint32_t, uint32_t> staging_;
+
+  // The full set of all committed items.
+  std::set<uint32_t> committed_;
+
+  DISALLOW_COPY_AND_ASSIGN(BlimpPictureCacheRegistry);
+};
+
+}  // namespace blimp
+
+#endif  // BLIMP_COMMON_COMPOSITOR_BLIMP_PICTURE_CACHE_REGISTRY_H_