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

chrome/browser/extensions/extension_host_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 "chrome/browser/extensions/extension_host_mac.h"
 
 #import "chrome/browser/ui/cocoa/chrome_event_processing_window.h"
 #import "chrome/browser/ui/cocoa/extensions/extension_popup_controller.h"
 #import "chrome/browser/ui/cocoa/info_bubble_window.h"
 #include "chrome/common/chrome_view_types.h"
 #include "content/browser/renderer_host/render_widget_host_view_mac.h"
 #include "content/public/browser/native_web_keyboard_event.h"
 
 ExtensionHostMac::~ExtensionHostMac() {
   // If there is a popup open for this host's extension, close it.
   ExtensionPopupController* popup = [ExtensionPopupController popup];
   if ([[popup window] isVisible] &&
       [popup extensionHost]->extension() == this->extension()) {
     InfoBubbleWindow* window = (InfoBubbleWindow*)[popup window];
     [window setDelayOnClose:NO];
     [popup close];
   }
 }
 
-RenderWidgetHostView* ExtensionHostMac::CreateNewWidgetInternal(
-    int route_id,
-    WebKit::WebPopupType popup_type) {
-  // A RenderWidgetHostViewMac has lifetime scoped to the view. We'll retain it
-  // to allow it to survive the trip without being hosed.
-  RenderWidgetHostView* widget_view =
-      ExtensionHost::CreateNewWidgetInternal(route_id, popup_type);
-  RenderWidgetHostViewMac* widget_view_mac =
-      static_cast<RenderWidgetHostViewMac*>(widget_view);
-  [widget_view_mac->native_view() retain];
-
-  return widget_view;
-}
-
-void ExtensionHostMac::ShowCreatedWidgetInternal(
-    RenderWidgetHostView* widget_host_view,
-    const gfx::Rect& initial_pos) {
-  ExtensionHost::ShowCreatedWidgetInternal(widget_host_view, initial_pos);
-
-  // A RenderWidgetHostViewMac has lifetime scoped to the view. Now that it's
-  // properly embedded (or purposefully ignored) we can release the reference we
-  // took in CreateNewWidgetInternal().
-  RenderWidgetHostViewMac* widget_view_mac =
-      static_cast<RenderWidgetHostViewMac*>(widget_host_view);
-  [widget_view_mac->native_view() release];
-}
-
 void ExtensionHostMac::UnhandledKeyboardEvent(
     const NativeWebKeyboardEvent& event) {
   if (event.skip_in_browser || event.type == NativeWebKeyboardEvent::Char ||
       extension_host_type() != chrome::VIEW_TYPE_EXTENSION_POPUP) {
     return;
   }
 
   ChromeEventProcessingWindow* event_window =
       static_cast<ChromeEventProcessingWindow*>([view()->native_view() window]);
   DCHECK([event_window isKindOfClass:[ChromeEventProcessingWindow class]]);
   [event_window redispatchKeyEvent:event.os_event];
 }