Move RFH's WeakPtrFactory to be the last member.

BUG=none

Review URL: https://codereview.chromium.org/589653002

Cr-Commit-Position: refs/heads/master@{#295777}

content/browser/frame_host/render_frame_host_impl.h

@@ -479,8 +479,6 @@ class CONTENT_EXPORT RenderFrameHostImpl
 
   ServiceRegistryImpl service_registry_;
 
-  base::WeakPtrFactory<RenderFrameHostImpl> weak_ptr_factory_;
-
   scoped_ptr<BrowserAccessibilityManager> browser_accessibility_manager_;
 
   // Callback when an event is received, for testing.
@@ -488,6 +486,9 @@ class CONTENT_EXPORT RenderFrameHostImpl
   // The most recently received accessibility tree - for testing only.
   scoped_ptr<ui::AXTree> ax_tree_for_testing_;
 
+  // NOTE: This must be the last member.
+  base::WeakPtrFactory<RenderFrameHostImpl> weak_ptr_factory_;
+
   DISALLOW_COPY_AND_ASSIGN(RenderFrameHostImpl);
 };