Add SurfaceWillDraw notification

cc/surfaces/surface_aggregator.cc

 // Copyright 2014 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/surfaces/surface_aggregator.h"
 
 #include <stddef.h>
 
 #include <map>
 
@@ skipping 744 matching lines @@
   for (const auto& surface_id : frame.metadata.referenced_surfaces) {
     if (!contained_surfaces_.count(surface_id)) {
       result->undrawn_surfaces.insert(surface_id);
       PrewalkTree(surface_id, false, 0, result);
     }
   }
 
   CHECK(debug_weak_this.get());
   // TODO(staraz): It shouldn't need to call the callback when the damage is
   // from |surface| and not from |child_surfaces|.
-  if (!damage_rect.IsEmpty())
+  if (!damage_rect.IsEmpty()) {
     surface->RunWillDrawCallback(damage_rect);
+    manager_->SurfaceWillDraw(surface->surface_id());

[danakj, 2017/06/14 18:53:12]

Would it be better to collect a set of surface ids and give them all in a single
callback? Would that let the consumer do smarter things? Will each user of the
callback have to do to the same otherwise?

[gklassen, 2017/06/14 19:29:11]

In the consumer we are currently contemplating it needs to do the same work for
each surface ( move the associated hit test data to an active list ) - so it
doesn't seem like it would provide much immediate benefit but we may want to
revisit later and if we add other consumers.    

+  }
 
   CHECK(debug_weak_this.get());
   for (const auto& render_pass : frame.render_pass_list) {
     if (!render_pass->copy_requests.empty()) {
       RenderPassId remapped_pass_id = RemapPassId(render_pass->id, surface_id);
       copy_request_passes_.insert(remapped_pass_id);
     }
   }
 
   referenced_surfaces_.erase(referenced_surfaces_.find(surface->surface_id()));
@@ skipping 157 matching lines @@
 }
 
 void SurfaceAggregator::SetOutputColorSpace(
     const gfx::ColorSpace& blending_color_space,
     const gfx::ColorSpace& output_color_space) {
   blending_color_space_ = blending_color_space;
   output_color_space_ = output_color_space;
 }
 
 }  // namespace cc