Add main thread scrolling reasons to GraphicsLayer::layerTreeAsJSON.

ui/compositor/layer.cc

 // Copyright (c) 2012 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 "ui/compositor/layer.h"
 
 #include <algorithm>
 #include <memory>
 #include <utility>
 
@@ skipping 798 matching lines @@
 
  private:
   std::string name_;
 };
 
 std::unique_ptr<base::trace_event::ConvertableToTraceFormat>
 Layer::TakeDebugInfo(cc::Layer* layer) {
   return base::WrapUnique(new LayerDebugInfo(name_));
 }
 
+void Layer::didUpdateMainThreadScrollingReasons() {}
+
 void Layer::CollectAnimators(
     std::vector<scoped_refptr<LayerAnimator>>* animators) {
   if (animator_ && animator_->is_animating())
     animators->push_back(animator_);
   for (auto* child : children_)
     child->CollectAnimators(animators);
 }
 
 void Layer::StackRelativeTo(Layer* child, Layer* other, bool above) {
   DCHECK_NE(child, other);
@@ skipping 229 matching lines @@
   if (animator_) {
     animator_->ResetCompositor(compositor);
     animator_->RemoveFromCollection(collection);
   }
 
   for (auto* child : children_)
     child->ResetCompositorForAnimatorsInTree(compositor);
 }
 
 }  // namespace ui