Add an option on SkImageDecoder to skip writing 0s.

tests/ImageDecodingTest.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 "SkBitmap.h"
 #include "SkCanvas.h"
 #include "SkColor.h"
@@ skipping 237 matching lines @@
             SkDebugf("could not build a tile index\n");
             continue;
         }
         // Now unref the stream to make sure it survives
         stream.reset(NULL);
         SkBitmap bm;
         decoder->decodeSubset(&bm, SkIRect::MakeWH(width, height),
                               SkBitmap::kARGB_8888_Config);
     }
 }
-#endif
+
+// Test inside SkScaledBitmapSampler.cpp
+extern void test_row_proc_choice();
+
+#endif // SK_DEBUG
 
 static void test_imageDecodingTests(skiatest::Reporter* reporter) {
     test_unpremul(reporter);
     test_pref_config_table(reporter);
 #ifdef SK_DEBUG
     test_stream_life();
+    test_row_proc_choice();
 #endif
 }
 
 #include "TestClassDef.h"
 DEFINE_TESTCLASS("ImageDecoding", ImageDecodingTestClass,
                  test_imageDecodingTests)