Implement SkAshmemDiscardableMemory

tools/LazyDecodeBitmap.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 "LazyDecodeBitmap.h"
 
 #include "SkData.h"
 #include "SkDecodingImageGenerator.h"
 #include "SkDiscardableMemoryPool.h"
 #include "SkDiscardablePixelRef.h"
 #include "SkForceLinking.h"
 
 #include "SkCommandLineFlags.h"
 
 __SK_FORCE_IMAGE_DECODER_LINKING;
 
-// TODO(halcanary) Use this flag when ashmem-backed discardable memory lands.
 DEFINE_bool(useVolatileCache, false, "Use a volatile cache for deferred image decoding pixels. "
             "Only meaningful if --deferImageDecoding is set to true and the platform has an "
             "implementation.");
 
 //  Fits SkPicture::InstallPixelRefProc call signature.
 //  Used in SkPicturePlayback::CreateFromStream
 bool sk_tools::LazyDecodeBitmap(const void* src,
                                 size_t length,
                                 SkBitmap* dst) {
     SkAutoDataUnref data(SkData::NewWithCopy(src, length));
     if (NULL == data.get()) {
         return false;
     }
 
     SkAutoTDelete<SkImageGenerator> gen(SkNEW_ARGS(SkDecodingImageGenerator,
                                                    (data)));
     SkImageInfo info;
     if (!gen->getInfo(&info)) {
         return false;
     }
     SkDiscardableMemory::Factory* pool = NULL;
-    if (info.fWidth * info.fHeight > 32 * 1024) {
+    if ((!FLAGS_useVolatileCache) || (info.fWidth * info.fHeight < 32 * 1024)) {
         // how to do switching with SkDiscardableMemory.
         pool = SkGetGlobalDiscardableMemoryPool();
+        // Only meaningful if platform has a default discardable
+        // memory implementation that differs from the global DM pool.
     }
     return SkDiscardablePixelRef::Install(gen.detach(), dst, pool);
 }