Option for SkCodec to treat dst as all zeroes.

tests/DrawBitmapRectTest.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 "SkBitmap.h"
 #include "SkCanvas.h"
 #include "SkData.h"
@@ skipping 10 matching lines @@
 class FailureImageGenerator : public SkImageGenerator {
 public:
     FailureImageGenerator() { }
     virtual ~FailureImageGenerator() { }
 
 protected:
     bool onGetInfo(SkImageInfo* info) SK_OVERRIDE {
         *info = SkImageInfo::MakeN32Premul(100, 100);
         return true;
     }
-    // default onGetPixels() returns false, which is what we want.
+    // default onGetPixels() returns kUnimplemented, which is what we want.
 };
 
 // crbug.com/295895
 // Crashing in skia when a pixelref fails in lockPixels
 //
 static void test_faulty_pixelref(skiatest::Reporter* reporter) {
     // need a cache, but don't expect to use it, so the budget is not critical
     SkAutoTUnref<SkDiscardableMemoryPool> pool(
         SkDiscardableMemoryPool::Create(10 * 1000, NULL));
     SkBitmap bm;
@@ skipping 267 matching lines @@
 
     // ensure that we draw nothing if srcR does not intersect the bitmap
     REPORTER_ASSERT(reporter, check_for_all_zeros(dst));
 
     test_nan_antihair();
     test_giantrepeat_crbug118018(reporter);
 
     test_treatAsSprite(reporter);
     test_faulty_pixelref(reporter);
 }