Add decode() functionality to image elements.

cc/trees/layer_tree_host_impl_unittest.cc

 // Copyright 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/trees/layer_tree_host_impl.h"
 
 #include <stddef.h>
 
 #include <algorithm>
 #include <cmath>
@@ skipping 173 matching lines @@
     EXPECT_EQ(DRAW_SUCCESS, host_impl_->PrepareToDraw(frame.get()));
     last_on_draw_render_passes_.clear();
     RenderPass::CopyAll(frame->render_passes, &last_on_draw_render_passes_);
     host_impl_->DrawLayers(frame.get());
     host_impl_->DidDrawAllLayers(*frame);
     last_on_draw_frame_ = std::move(frame);
   }
   void NeedsImplSideInvalidation() override {
     did_request_impl_side_invalidation_ = true;
   }
+  void NotifyImageDecodeRequestFinished() override {}
 
   void set_reduce_memory_result(bool reduce_memory_result) {
     reduce_memory_result_ = reduce_memory_result;
   }
 
   virtual bool CreateHostImpl(
       const LayerTreeSettings& settings,
       std::unique_ptr<CompositorFrameSink> compositor_frame_sink) {
     return CreateHostImplWithTaskRunnerProvider(
         settings, std::move(compositor_frame_sink), &task_runner_provider_);
@@ skipping 12166 matching lines @@
     else
       EXPECT_FALSE(tile->HasRasterTask());
   }
   Region expected_invalidation(
       raster_source->GetRectForImage(checkerable_image->uniqueID()));
   EXPECT_EQ(expected_invalidation, *(root->GetPendingInvalidation()));
 }
 
 }  // namespace
 }  // namespace cc