Fix tab switch time regression from backgrounded renderers change

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 891 matching lines @@
       ui::TAB_SHOW_COMPONENT,
       render_widget_host_->GetLatencyComponentId(),
       0);
   render_widget_host_->WasShown(renderer_latency_info);
 }
 
 void RenderWidgetHostViewMac::WasOccluded() {
   if (render_widget_host_->is_hidden())
     return;
 
+  // SuspendBrowserCompositorView() instructs the GPU process to free up
+  // resources such as textures. WasHidden() places the renderer process in the
+  // background and throttles its I/O. We're cafeful to call WasHidden() only
+  // after calling SuspendBrowserCompositorView(), otherwise the backgrounded
+  // and throttled renderer's communication with GPU process will take extra
+  // time to complete. The delay will block the foreground renderer's
+  // communication with the GPU process, resulting in longer tab switching
+  // time. http://crbug.com/502502 .
+  SuspendBrowserCompositorView();
   render_widget_host_->WasHidden();
-  SuspendBrowserCompositorView();
 }
 
 void RenderWidgetHostViewMac::SetSize(const gfx::Size& size) {
   gfx::Rect rect = GetViewBounds();
   rect.set_size(size);
   SetBounds(rect);
 }
 
 void RenderWidgetHostViewMac::SetBounds(const gfx::Rect& rect) {
   // |rect.size()| is view coordinates, |rect.origin| is screen coordinates,
@@ skipping 2366 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