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 "SkMask.h"
+#include "SkRect.h"
+#include "SkRRect.h"
+#include "SkScaledImageCache.h"
+
+class SkMaskCache {
+public:
+    typedef SkScaledImageCache::ID ID;
+
+    static void Unlock(ID* id) {
+        SkScaledImageCache::Unlock(id);
+    }
+
+    /* Input: blur_sigma+rrect */
+    static ID* FindAndLock(SkScalar sigma, const SkRRect rrect, SkMask* result);
+    static ID* AddAndLock(SkScalar sigma, const SkRRect rrect, const SkMask& mask);
+
+    /* Input: blur_sigma+rects_count+rects */
+    static ID* FindAndLock(SkScalar sigma, unsigned count, const SkRect rects[],
+                           SkMask* result);
+    static ID* AddAndLock(SkScalar sigma, unsigned count, const SkRect rects[],
+                          const SkMask& mask);
+};
+
+#endif