Remove image_decode_tasks_enabled flag.

cc/layers/picture_layer.cc

Index: cc/layers/picture_layer.cc
diff --git a/cc/layers/picture_layer.cc b/cc/layers/picture_layer.cc
index 68e92f74f9ffacb7a84a055c46b21ab1b93980e1..f22545cc29f605786eb284dd54d8cb781c49dba4 100644
--- a/cc/layers/picture_layer.cc
+++ b/cc/layers/picture_layer.cc
@@ -83,11 +83,6 @@ void PictureLayer::SetLayerTreeHost(LayerTreeHost* host) {
     recording_source_.reset(new RecordingSource);
   recording_source_->SetSlowdownRasterScaleFactor(
       host->GetDebugState().slow_down_raster_scale_factor);
-  // If we need to enable image decode tasks, then we have to generate the
-  // discardable images metadata.
-  const LayerTreeSettings& settings = layer_tree_host()->GetSettings();
-  recording_source_->SetGenerateDiscardableImagesMetadata(
-      settings.image_decode_tasks_enabled);
 }
 
 void PictureLayer::SetNeedsDisplayRect(const gfx::Rect& layer_rect) {