Use preferred format to allocate memory for decoded images

cc/tiles/software_image_decode_controller.h

Index: cc/tiles/software_image_decode_controller.h
diff --git a/cc/tiles/software_image_decode_controller.h b/cc/tiles/software_image_decode_controller.h
index 7e370bb8cb8c1c87e1b5f8888cd1075700824695..20dc4511f23a95e0a97fc77ef29c396c987fcf17 100644
--- a/cc/tiles/software_image_decode_controller.h
+++ b/cc/tiles/software_image_decode_controller.h
@@ -96,7 +96,7 @@ class CC_EXPORT SoftwareImageDecodeController : public ImageDecodeController {
   using ImageKey = ImageDecodeControllerKey;
   using ImageKeyHash = ImageDecodeControllerKeyHash;
 
-  SoftwareImageDecodeController();
+  explicit SoftwareImageDecodeController(ResourceFormat format = RGBA_8888);

[vmpstr, 2016/03/21 20:00:45]

Default parameters are prohibited in Chromium.

   ~SoftwareImageDecodeController() override;
 
   // ImageDecodeController overrides.
@@ -221,6 +221,8 @@ class CC_EXPORT SoftwareImageDecodeController : public ImageDecodeController {
   // image the first time we see it. This mimics the previous behavior and
   // should over time change as the compositor starts to handle more cases.
   std::unordered_set<uint32_t> prerolled_images_;
+
+  ResourceFormat format_;
 };
 
 }  // namespace cc