Optimize CSS box-shadow performance by caching the SkMask of the blur effect.

src/core/SkScaledImageCache.cpp

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkScaledImageCache.h"
 #include "SkMipMap.h"
 #include "SkPixelRef.h"
@@ skipping 258 matching lines @@
     if (0 == size) {
         return false;
     }
 
     SkDiscardableMemory* dm = fFactory(size);
     if (NULL == dm) {
         return false;
     }
 
     // can we relax this?
-    if (kN32_SkColorType != bitmap->colorType()) {
+    if (kN32_SkColorType != bitmap->colorType()
+        && kAlpha_8_SkColorType != bitmap->colorType()) {
         return false;
     }
 
     SkImageInfo info = bitmap->info();
     bitmap->setPixelRef(SkNEW_ARGS(SkOneShotDiscardablePixelRef,
                                    (info, dm, bitmap->rowBytes())))->unref();
     bitmap->lockPixels();
     return bitmap->readyToDraw();
 }
 
@@ skipping 484 matching lines @@
     return SkScaledImageCache::GetBytesUsed();
 }
 
 size_t SkGraphics::GetImageCacheByteLimit() {
     return SkScaledImageCache::GetByteLimit();
 }
 
 size_t SkGraphics::SetImageCacheByteLimit(size_t newLimit) {
     return SkScaledImageCache::SetByteLimit(newLimit);
 }