Force software layer to redraw when it is resized.

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 <QuartzCore/QuartzCore.h>
 
 #include "base/basictypes.h"
@@ skipping 2259 matching lines @@
     if (software_frame_manager_->GetCurrentFrameDeviceScaleFactor() !=
         [software_layer_ contentsScale]) {
       [software_layer_ setContentsScale:
           software_frame_manager_->GetCurrentFrameDeviceScaleFactor()];
     }
   }
   // Changing the software layer's bounds and position doesn't always result
   // in the layer being anchored to the top-left. Set the layer's frame
   // explicitly, since this is more reliable in practice.
   if (software_layer_) {
-    [software_layer_ setFrame:new_background_frame];
+    bool frame_changed = !CGRectEqualToRect(
+        new_background_frame, [software_layer_ frame]);
+    if (frame_changed) {
+      [software_layer_ setFrame:new_background_frame];
+      [software_layer_ setNeedsDisplay];
+    }
   }
 }
 
 SkBitmap::Config RenderWidgetHostViewMac::PreferredReadbackFormat() {
   return SkBitmap::kARGB_8888_Config;
 }
 
 }  // namespace content
 
 // RenderWidgetHostViewCocoa ---------------------------------------------------
@@ skipping 2021 matching lines @@
 }
 
 - (void)disableRendering {
   // Disable the fade-out animation as the layer is removed.
   ScopedCAActionDisabler disabler;
   [self removeFromSuperlayer];
   renderWidgetHostView_ = nil;
 }
 
 @end  // implementation SoftwareLayer