Add medium image quality to software predecode.

cc/tiles/software_image_decode_controller_unittest.cc

Index: cc/tiles/software_image_decode_controller_unittest.cc
diff --git a/cc/tiles/software_image_decode_controller_unittest.cc b/cc/tiles/software_image_decode_controller_unittest.cc
index 6374bce01fc5131140c82baacfdb3e7c2a1fc725..9be2866f0a7b9c23df158c602e9a4671ce3160b7 100644
--- a/cc/tiles/software_image_decode_controller_unittest.cc
+++ b/cc/tiles/software_image_decode_controller_unittest.cc
@@ -403,10 +403,7 @@ TEST(SoftwareImageDecodeControllerTest,
   scoped_refptr<TileTask> medium_quality_task;
   need_unref = controller.GetTaskForImageAndRef(
       medium_quality_draw_image, prepare_tiles_id, &medium_quality_task);
-  // Medium quality isn't handled by the controller, so it won't ref it. Note
-  // that this will change when medium quality is handled and will need to be
-  // updated.
-  EXPECT_FALSE(need_unref);
+  EXPECT_TRUE(need_unref);
   EXPECT_TRUE(medium_quality_task);
   EXPECT_TRUE(high_quality_task.get() != medium_quality_task.get());
 
@@ -423,6 +420,7 @@ TEST(SoftwareImageDecodeControllerTest,
   EXPECT_TRUE(medium_quality_task.get() != low_quality_task.get());
 
   controller.UnrefImage(high_quality_draw_image);
+  controller.UnrefImage(medium_quality_draw_image);
   controller.UnrefImage(low_quality_draw_image);
 }