Allow ui::Compositor to disable commits during tab-switch

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 <objc/runtime.h>
 #include <OpenGL/gl.h>
 #include <QuartzCore/QuartzCore.h>
 
@@ skipping 597 matching lines @@
     browser_compositor_->compositor()->SetHostHasTransparentBackground(
         !GetBackgroundOpaque());
     browser_compositor_->accelerated_widget_mac()->SetNSView(this);
     browser_compositor_state_ = BrowserCompositorSuspended;
   }
 
   // Show the DelegatedFrameHost to transition from Suspended -> Active.
   if (browser_compositor_state_ == BrowserCompositorSuspended) {
     delegated_frame_host_->SetCompositor(browser_compositor_->compositor());
     delegated_frame_host_->WasShown(ui::LatencyInfo());
+    browser_compositor_->compositor()->SetDeferCommits(false);
     browser_compositor_state_ = BrowserCompositorActive;
   }
 }
 
 void RenderWidgetHostViewMac::SuspendBrowserCompositorView() {
   TRACE_EVENT0("browser",
                "RenderWidgetHostViewMac::SuspendBrowserCompositorView");
 
   // Hide the DelegatedFrameHost to transition from Active -> Suspended.
   if (browser_compositor_state_ == BrowserCompositorActive) {
+    // Ensure that any changes made to the ui::Compositor do not result in new
+    // frames being produced. Note that this does not ensure that
+    // already-in-flight frames will be aborted.
+    browser_compositor_->compositor()->SetDeferCommits(true);
     // Marking the DelegatedFrameHost as removed from the window hierarchy is
     // necessary to remove all connections to its old ui::Compositor.
     delegated_frame_host_->WasHidden();
     delegated_frame_host_->ResetCompositor();
     browser_compositor_state_ = BrowserCompositorSuspended;
   }
 }
 
 void RenderWidgetHostViewMac::DestroyBrowserCompositorView() {
   TRACE_EVENT0("browser",
@@ skipping 2795 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