Initialize SkImage memory in gpu_image_decode_cache_unittest

cc/tiles/gpu_image_decode_cache_unittest.cc

Index: cc/tiles/gpu_image_decode_cache_unittest.cc
diff --git a/cc/tiles/gpu_image_decode_cache_unittest.cc b/cc/tiles/gpu_image_decode_cache_unittest.cc
index 91a08d1f40ce4e497ee851d826b9e23f08db5677..123f84dcd23f8006f4a1058bc285d91084234cca 100644
--- a/cc/tiles/gpu_image_decode_cache_unittest.cc
+++ b/cc/tiles/gpu_image_decode_cache_unittest.cc
@@ -32,6 +32,7 @@ sk_sp<SkImage> CreateImage(int width, int height) {
   gfx::ColorSpace color_space = gfx::ColorSpace::CreateSRGB();
   bitmap.allocPixels(
       SkImageInfo::MakeN32Premul(width, height, color_space.ToSkColorSpace()));
+  bitmap.eraseColor(0);
   return SkImage::MakeFromBitmap(bitmap);
 }