Have ExtensionHost use TabContents instead of RenderViewHost. Try #3.

content/browser/renderer_host/render_widget_host_view_mac.mm

 // Copyright (c) 2011 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"
 
 #include <QuartzCore/QuartzCore.h>
 
 #include "base/bind.h"
 #include "base/debug/trace_event.h"
@@ skipping 1652 matching lines @@
 }
 
 - (void)setFrameSize:(NSSize)newSize {
   // NB: -[NSView setFrame:] calls through -setFrameSize:, so overriding
   // -setFrame: isn't neccessary.
   [super setFrameSize:newSize];
   if (renderWidgetHostView_->render_widget_host_)
     renderWidgetHostView_->render_widget_host_->WasResized();
 }
 
-- (void)setFrameWithDeferredUpdate:(NSRect)frameRect {
-  [super setFrame:frameRect];
-  [self performSelector:@selector(renderWidgetHostWasResized)
-             withObject:nil
-             afterDelay:0];
-}
-
-- (void)renderWidgetHostWasResized {
-  if (renderWidgetHostView_->render_widget_host_)
-    renderWidgetHostView_->render_widget_host_->WasResized();
-}
-
 - (void)callSetNeedsDisplayInRect {
   DCHECK([NSThread isMainThread]);
   DCHECK(renderWidgetHostView_->call_set_needs_display_in_rect_pending_);
   [self setNeedsDisplayInRect:renderWidgetHostView_->invalid_rect_];
   renderWidgetHostView_->call_set_needs_display_in_rect_pending_ = false;
   renderWidgetHostView_->invalid_rect_ = NSZeroRect;
 
   renderWidgetHostView_->HandleDelayedGpuViewHiding();
 }
 
@@ skipping 1062 matching lines @@
   if (!string) return NO;
 
   // If the user is currently using an IME, confirm the IME input,
   // and then insert the text from the service, the same as TextEdit and Safari.
   [self confirmComposition];
   [self insertText:string];
   return YES;
 }
 
 @end