Update GatherPixelRefDevice to the new SkImage/SkPixelRef API

cc/playback/display_list_raster_source_unittest.cc

Index: cc/playback/display_list_raster_source_unittest.cc
diff --git a/cc/playback/display_list_raster_source_unittest.cc b/cc/playback/display_list_raster_source_unittest.cc
index 4e8a783a976865435a6541cfe5a8d0bee56cb033..922ba00a9296fe3367592fde9bd4a26feb9d7dea 100644
--- a/cc/playback/display_list_raster_source_unittest.cc
+++ b/cc/playback/display_list_raster_source_unittest.cc
@@ -176,9 +176,9 @@ TEST(DisplayListRasterSourceTest, PixelRefIteratorDiscardableRefsOneTile) {
       FakeDisplayListRecordingSource::CreateFilledRecordingSource(layer_bounds);
 
   SkBitmap discardable_bitmap[2][2];
-  CreateBitmap(gfx::Size(32, 32), "discardable", &discardable_bitmap[0][0]);
-  CreateBitmap(gfx::Size(32, 32), "discardable", &discardable_bitmap[0][1]);
-  CreateBitmap(gfx::Size(32, 32), "discardable", &discardable_bitmap[1][1]);
+  CreateDiscardableBitmap(gfx::Size(32, 32), &discardable_bitmap[0][0]);
+  CreateDiscardableBitmap(gfx::Size(32, 32), &discardable_bitmap[0][1]);
+  CreateDiscardableBitmap(gfx::Size(32, 32), &discardable_bitmap[1][1]);
 
   // Discardable pixel refs are found in the following cells:
   // |---|---|