Add an option on SkImageDecoder to skip writing 0s.

src/images/SkImageRef_ashmem.cpp

 
 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 #include "SkImageRef_ashmem.h"
 #include "SkImageDecoder.h"
 #include "SkFlattenableBuffers.h"
@@ skipping 116 matching lines @@
 };
 
 bool SkImageRef_ashmem::onDecode(SkImageDecoder* codec, SkStream* stream,
                                  SkBitmap* bitmap, SkBitmap::Config config,
                                  SkImageDecoder::Mode mode) {
 
     if (SkImageDecoder::kDecodeBounds_Mode == mode) {
         return this->INHERITED::onDecode(codec, stream, bitmap, config, mode);
     }
 
+    // Ashmem memory is guaranteed to be initialized to 0.
+    codec->setSkipWritingZeroes(true);
+
     AshmemAllocator alloc(&fRec, this->getURI());
 
     codec->setAllocator(&alloc);
     bool success = this->INHERITED::onDecode(codec, stream, bitmap, config,
                                              mode);
     // remove the allocator, since its on the stack
     codec->setAllocator(NULL);
 
     if (success) {
         // remember the colortable (if any)
@@ skipping 74 matching lines @@
     fRec.fFD = -1;
     fRec.fAddr = NULL;
     fRec.fSize = 0;
     fRec.fPinned = false;
     fCT = NULL;
 
     SkString uri;
     buffer.readString(&uri);
     this->setURI(uri);
 }