Initialize SkImage memory in gpu_image_decode_cache_unittest

cc/tiles/gpu_image_decode_cache_unittest.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/tiles/gpu_image_decode_cache.h"
 
 #include "cc/paint/draw_image.h"
 #include "cc/test/test_context_provider.h"
 #include "cc/test/test_tile_task_runner.h"
 #include "testing/gtest/include/gtest/gtest.h"
@@ skipping 14 matching lines @@
                             ResourceFormat::RGBA_8888,
                             kGpuMemoryLimitBytes,
                             kGpuMemoryLimitBytes) {}
 };
 
 sk_sp<SkImage> CreateImage(int width, int height) {
   SkBitmap bitmap;
   gfx::ColorSpace color_space = gfx::ColorSpace::CreateSRGB();
   bitmap.allocPixels(
       SkImageInfo::MakeN32Premul(width, height, color_space.ToSkColorSpace()));
+  bitmap.eraseColor(0);
   return SkImage::MakeFromBitmap(bitmap);
 }
 
 SkMatrix CreateMatrix(const SkSize& scale, bool is_decomposable) {
   SkMatrix matrix;
   matrix.setScale(scale.width(), scale.height());
 
   if (!is_decomposable) {
     // Perspective is not decomposable, add it.
     matrix[SkMatrix::kMPersp0] = 0.1f;
@@ skipping 1799 matching lines @@
   TestTileTaskRunner::ProcessTask(second_task->dependencies()[0].get());
   TestTileTaskRunner::ProcessTask(second_task.get());
 
   cache.UnrefImage(first_draw_image);
   cache.UnrefImage(second_draw_image);
   cache.UnrefImage(third_draw_image);
 }
 
 }  // namespace
 }  // namespace cc