Optimize CSS box-shadow performance

src/core/SkMaskCache.h

+/*
+ * Copyright 2014 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef SkMaskCache_DEFINED
+#define SkMaskCache_DEFINED
+
+#include "SkCachedData.h"
+#include "SkMask.h"
+#include "SkRect.h"
+#include "SkRRect.h"
+
+class SkMaskCache {
+public:
+    /**
+     * On success, return a ref to the SkCachedData that holds the pixels, and have mask
+     * already point to that memory.
+     *
+     * On failure, return NULL.
+     */
+    static SkCachedData* FindAndRef(SkScalar sigma, const SkRRect& rrect, SkMask* mask);
+    static void Add(SkScalar sigma, const SkRRect& rrect,
+                    const SkMask& mask, SkCachedData* data);
+
+    /**
+     * On success, return a ref to the SkCachedData that holds the pixels, and have mask
+     * already point to that memory.
+     *
+     * On failure, return NULL.
+     */
+    static SkCachedData* FindAndRef(SkScalar sigma, int32_t count,
+                                    const SkRect rects[], SkMask* mask);
+    static void Add(SkScalar sigma, int32_t count, const SkRect rects[],
+                    const SkMask& mask, SkCachedData* data);
+};
+
+#endif