Add Mojo API for Blink hit testing

components/viz/service/frame_sinks/direct_layer_tree_frame_sink.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 "components/viz/service/frame_sinks/direct_layer_tree_frame_sink.h"
 
 #include "base/bind.h"
 #include "cc/output/compositor_frame.h"
 #include "cc/output/layer_tree_frame_sink_client.h"
 #include "components/viz/common/surfaces/frame_sink_id.h"
@@ skipping 57 matching lines @@
 
   // We want the Display's output surface to hear about lost context, and since
   // this shares a context with it, we should not be listening for lost context
   // callbacks on the context here.
   if (auto* cp = context_provider())
     cp->SetLostContextCallback(base::Closure());
 
   constexpr bool is_root = true;
   constexpr bool handles_frame_sink_id_invalidation = false;
   support_ = support_manager_->CreateCompositorFrameSinkSupport(
-      this, frame_sink_id_, is_root, handles_frame_sink_id_invalidation,
+      this, nullptr, frame_sink_id_, is_root,

[Navid Zolghadr, 2017/08/09 16:08:22]

There are some places like this that were not being reached as the result of
CreateForWidget. So I wouldn't have the hit test interface instance. I wasn't
sure what to do with these and when each of those cases happen. Any idea?

+      handles_frame_sink_id_invalidation,
       capabilities_.delegated_sync_points_required);
   begin_frame_source_ = base::MakeUnique<ExternalBeginFrameSource>(this);
   client_->SetBeginFrameSource(begin_frame_source_.get());
 
   // Avoid initializing GL context here, as this should be sharing the
   // Display's context.
   display_->Initialize(this, frame_sink_manager_->surface_manager());
   return true;
 }
 
@@ skipping 74 matching lines @@
 
 void DirectLayerTreeFrameSink::OnBeginFramePausedChanged(bool paused) {
   begin_frame_source_->OnSetBeginFrameSourcePaused(paused);
 }
 
 void DirectLayerTreeFrameSink::OnNeedsBeginFrames(bool needs_begin_frame) {
   support_->SetNeedsBeginFrame(needs_begin_frame);
 }
 
 }  // namespace viz