Centralize FrameSinkId allocation in one place

content/browser/renderer_host/render_widget_host_view_mac.mm

 // 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 "content/browser/renderer_host/render_widget_host_view_mac.h"
 
 #import <Carbon/Carbon.h>
 #import <objc/runtime.h>
 #include <OpenGL/gl.h>
 #include <QuartzCore/QuartzCore.h>
@@ skipping 452 matching lines @@
 
   // Paint this view host with |background_color_| when there is no content
   // ready to draw.
   background_layer_.reset([[CALayer alloc] init]);
   // Set the default color to be white. This is the wrong thing to do, but many
   // UI components expect this view to be opaque.
   [background_layer_ setBackgroundColor:CGColorGetConstantColor(kCGColorWhite)];
   [cocoa_view_ setLayer:background_layer_];
   [cocoa_view_ setWantsLayer:YES];
 
-  // GuestViews have two RenderWidgetHostViews and so we need to make sure
-  // we don't have FrameSinkId collisions.
-  // The FrameSinkId generated here must be unique with FrameSinkId allocated
-  // in ContextFactoryPrivate.
-  // TODO(crbug.com/685777): Centralize allocation in one place for easier
-  // maintenance.
-  ImageTransportFactory* factory = ImageTransportFactory::GetInstance();
   cc::FrameSinkId frame_sink_id =
-      is_guest_view_hack_
-          ? factory->GetContextFactoryPrivate()->AllocateFrameSinkId()
-          : cc::FrameSinkId(base::checked_cast<uint32_t>(
-                                render_widget_host_->GetProcess()->GetID()),
-                            base::checked_cast<uint32_t>(
-                                render_widget_host_->GetRoutingID()));
+      render_widget_host_->AllocateFrameSinkId(is_guest_view_hack_);
   browser_compositor_.reset(
       new BrowserCompositorMac(this, this, render_widget_host_->is_hidden(),
                                [cocoa_view_ window], frame_sink_id));
 
   display::Screen::GetScreen()->AddObserver(this);
 
   if (!is_guest_view_hack_)
     render_widget_host_->SetView(this);
 
   // Let the page-level input event router know about our surface ID
@@ skipping 2976 matching lines @@
 
 // "-webkit-app-region: drag | no-drag" is implemented on Mac by excluding
 // regions that are not draggable. (See ControlRegionView in
 // native_app_window_cocoa.mm). This requires the render host view to be
 // draggable by default.
 - (BOOL)mouseDownCanMoveWindow {
   return YES;
 }
 
 @end