Reduce SurfaceIdAllocator usage and tie SurfaceFactory to a single FrameSinkId

services/ui/surfaces/display_compositor.cc

Index: services/ui/surfaces/display_compositor.cc
diff --git a/services/ui/surfaces/display_compositor.cc b/services/ui/surfaces/display_compositor.cc
index 4603eacc0d549f2bb7da3ca64310a9519d663ecf..04db575df31879e85ca710eece2bc21ded573757 100644
--- a/services/ui/surfaces/display_compositor.cc
+++ b/services/ui/surfaces/display_compositor.cc
@@ -29,13 +29,14 @@ DisplayCompositor::DisplayCompositor(
     gfx::AcceleratedWidget widget,
     scoped_refptr<gpu::GpuChannelHost> gpu_channel,
     const scoped_refptr<SurfacesState>& surfaces_state)
-    : task_runner_(task_runner),
+    : frame_sink_id_(surfaces_state->next_client_id(), 0),
+      task_runner_(task_runner),
       surfaces_state_(surfaces_state),
-      factory_(surfaces_state->manager(), this),
-      allocator_(cc::FrameSinkId(surfaces_state->next_client_id(), 0)) {
-  surfaces_state_->manager()->RegisterFrameSinkId(allocator_.frame_sink_id());
-  surfaces_state_->manager()->RegisterSurfaceFactoryClient(
-      allocator_.frame_sink_id(), this);
+      allocator_(frame_sink_id_),
+      factory_(frame_sink_id_, surfaces_state->manager(), this) {
+  surfaces_state_->manager()->RegisterFrameSinkId(frame_sink_id_);
+  surfaces_state_->manager()->RegisterSurfaceFactoryClient(frame_sink_id_,
+                                                           this);
 
   gpu::GpuMemoryBufferManager* gpu_memory_buffer_manager =
       gpu_channel->gpu_memory_buffer_manager();
@@ -75,15 +76,13 @@ DisplayCompositor::DisplayCompositor(
       cc::RendererSettings(), std::move(synthetic_begin_frame_source),
       std::move(display_output_surface), std::move(scheduler),
       base::MakeUnique<cc::TextureMailboxDeleter>(task_runner_.get())));
-  display_->Initialize(this, surfaces_state_->manager(),
-                       allocator_.frame_sink_id());
+  display_->Initialize(this, surfaces_state_->manager(), frame_sink_id_);
   display_->SetVisible(true);
 }
 
 DisplayCompositor::~DisplayCompositor() {
-  surfaces_state_->manager()->UnregisterSurfaceFactoryClient(
-      allocator_.frame_sink_id());
-  surfaces_state_->manager()->InvalidateFrameSinkId(allocator_.frame_sink_id());
+  surfaces_state_->manager()->UnregisterSurfaceFactoryClient(frame_sink_id_);
+  surfaces_state_->manager()->InvalidateFrameSinkId(frame_sink_id_);
 }
 
 void DisplayCompositor::SubmitCompositorFrame(