Remove image_decode_tasks_enabled flag.

cc/raster/raster_source_unittest.cc

Index: cc/raster/raster_source_unittest.cc
diff --git a/cc/raster/raster_source_unittest.cc b/cc/raster/raster_source_unittest.cc
index 344205714c4b8b6242f423a01f8ff28d1e2f952b..5cb06aaf7c32adf2f08d32b56df0e04a17a341c2 100644
--- a/cc/raster/raster_source_unittest.cc
+++ b/cc/raster/raster_source_unittest.cc
@@ -207,7 +207,6 @@ TEST(RasterSourceTest, PixelRefIteratorDiscardableRefsOneTile) {
   recording_source->add_draw_image(discardable_image[0][1], gfx::Point(260, 0));
   recording_source->add_draw_image(discardable_image[1][1],
                                    gfx::Point(260, 260));
-  recording_source->SetGenerateDiscardableImagesMetadata(true);
   recording_source->Rerecord();
 
   scoped_refptr<RasterSource> raster =
@@ -593,7 +592,6 @@ TEST(RasterSourceTest, ImageHijackCanvasRespectsSharedCanvasTransform) {
   recording_source->add_draw_rect_with_flags(
       gfx::Rect(size.width() - 4, size.height() - 4, 4, 4), flags);
 
-  recording_source->SetGenerateDiscardableImagesMetadata(true);
   recording_source->Rerecord();
 
   bool can_use_lcd = true;