[Android] Avoid using ContentViewCore when detaching from RWHVAndroid

content/browser/renderer_host/render_widget_host_view_android.h

 // 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.
 
 #ifndef CONTENT_BROWSER_RENDERER_HOST_RENDER_WIDGET_HOST_VIEW_ANDROID_H_
 #define CONTENT_BROWSER_RENDERER_HOST_RENDER_WIDGET_HOST_VIEW_ANDROID_H_
 
 #include <map>
 #include <queue>
 
@@ skipping 312 matching lines @@
   bool use_surfaces_;
 
   // Used to control action dispatch at the next |OnVSync()| call.
   uint32 outstanding_vsync_requests_;
 
   bool is_showing_;
 
   // ContentViewCoreImpl is our interface to the view system.
   ContentViewCoreImpl* content_view_core_;
 
+  // Cache the WindowAndroid instance exposed by ContentViewCore to avoid
+  // calling into ContentViewCore when it is being detached from the
+  // WebContents during destruction. The WindowAndroid has stronger lifetime
+  // guarantees, and should be safe to use for observer detachment.
+  // This will be valid iff |content_view_core_| is valid.
+  ui::WindowAndroid* content_view_core_window_android_;

[jdduke (slow), 2015/04/28 18:38:01]

I'm not married to this name.

|current_window_android_|? |active_window_android_|? |content_view_window_|?

+
   ImeAdapterAndroid ime_adapter_android_;
 
   // Body background color of the underlying document.
   SkColor cached_background_color_;
 
   scoped_refptr<cc::DelegatedFrameResourceCollection> resource_collection_;
   scoped_refptr<cc::DelegatedFrameProvider> frame_provider_;
   scoped_refptr<cc::Layer> layer_;
 
   scoped_ptr<cc::SurfaceIdAllocator> id_allocator_;
@@ skipping 56 matching lines @@
   gfx::Vector2dF last_scroll_offset_;
 
   base::WeakPtrFactory<RenderWidgetHostViewAndroid> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(RenderWidgetHostViewAndroid);
 };
 
 } // namespace content
 
 #endif  // CONTENT_BROWSER_RENDERER_HOST_RENDER_WIDGET_HOST_VIEW_ANDROID_H_