Centralize FrameSinkId allocation in one place

content/browser/compositor/gpu_process_transport_factory.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 "content/browser/compositor/gpu_process_transport_factory.h"
 
 #include <string>
 #include <utility>
 
 #include "base/bind.h"
@@ skipping 671 matching lines @@
 ui::ContextFactory* GpuProcessTransportFactory::GetContextFactory() {
   return this;
 }
 
 ui::ContextFactoryPrivate*
 GpuProcessTransportFactory::GetContextFactoryPrivate() {
   return this;
 }
 
 cc::FrameSinkId GpuProcessTransportFactory::AllocateFrameSinkId() {
-  // The FrameSinkId generated here must be unique with

[danakj, 2017/02/15 20:18:10]

This comment goes away, but we lose any notion of the importance that this
doesn't collide with RenderWidgetHostImpl, which seems bad. It's also not
tracable in the code anymore.

How can we make the code actually enforce this instead, or connect it back to a
place that understands it at least, like we do here?

[xlai (Olivia), 2017/02/15 22:38:36]

Done. I added the comment back in places where FrameSinkIdAllocator is
constructed.

-  // RenderWidgetHostViewAura's
-  // and RenderWidgetHostViewMac's FrameSinkId allocation.
-  // TODO(crbug.com/685777): Centralize allocation in one place for easier
-  // maintenance.
-  return cc::FrameSinkId(0, next_sink_id_++);
+  return frame_sink_id_allocator_.NextFrameSinkId();
 }
 
 void GpuProcessTransportFactory::SetDisplayVisible(ui::Compositor* compositor,
                                                    bool visible) {
   PerCompositorDataMap::iterator it = per_compositor_data_.find(compositor);
   if (it == per_compositor_data_.end())
     return;
   PerCompositorData* data = it->second.get();
   DCHECK(data);
   // The compositor will always SetVisible on the Display once it is set up, so
@@ skipping 206 matching lines @@
       shared_vulkan_context_provider_ =
           cc::VulkanInProcessContextProvider::Create();
     }
 
     shared_vulkan_context_provider_initialized_ = true;
   }
   return shared_vulkan_context_provider_;
 }
 
 }  // namespace content