Add decode() functionality to image elements.

cc/test/fake_layer_tree_host_impl_client.h

Index: cc/test/fake_layer_tree_host_impl_client.h
diff --git a/cc/test/fake_layer_tree_host_impl_client.h b/cc/test/fake_layer_tree_host_impl_client.h
index 4dd405ddab916bb966146d35edbee2704da9a622..2006d5d450aa3ce114e24fad0d05ae42f2da188a 100644
--- a/cc/test/fake_layer_tree_host_impl_client.h
+++ b/cc/test/fake_layer_tree_host_impl_client.h
@@ -36,6 +36,7 @@ class FakeLayerTreeHostImplClient : public LayerTreeHostImplClient {
   void DidCompletePageScaleAnimationOnImplThread() override {}
   void OnDrawForCompositorFrameSink(bool resourceless_software_draw) override {}
   void NeedsImplSideInvalidation() override;
+  void NotifyImageDecodeRequestFinished() override {}
 
   void reset_did_request_impl_side_invalidation() {
     did_request_impl_side_invalidation_ = false;