Add histogram for how tab closing time. Did some cleanup along the way.

chrome/browser/renderer_host/render_view_host_delegate.h

 // Copyright (c) 2009 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 CHROME_BROWSER_RENDERER_HOST_RENDER_VIEW_HOST_DELEGATE_H_
 #define CHROME_BROWSER_RENDERER_HOST_RENDER_VIEW_HOST_DELEGATE_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 427 matching lines @@
   virtual void UpdateInspectorSettings(const std::string& raw_settings) {}
 
   // The page is trying to close the RenderView's representation in the client.
   virtual void Close(RenderViewHost* render_view_host) {}
 
   // The page is trying to move the RenderView's representation in the client.
   virtual void RequestMove(const gfx::Rect& new_bounds) {}
 
   // The RenderView began loading a new page. This corresponds to WebKit's
   // notion of the throbber starting.
-  virtual void DidStartLoading(RenderViewHost* render_view_host) {}
+  virtual void DidStartLoading() {}
 
   // The RenderView stopped loading a page. This corresponds to WebKit's
   // notion of the throbber stopping.
-  virtual void DidStopLoading(RenderViewHost* render_view_host) {}
+  virtual void DidStopLoading() {}
 
   // The RenderView's main frame document element is ready. This happens when
   // the document has finished parsing.
   virtual void DocumentAvailableInMainFrame(RenderViewHost* render_view_host) {}
 
   // The page wants to open a URL with the specified disposition.
   virtual void RequestOpenURL(const GURL& url,
                               const GURL& referrer,
                               WindowOpenDisposition disposition) {}
 
@@ skipping 88 matching lines @@
   virtual bool IsExternalTabContainer() const;
 
   // The RenderView has inserted one css file into page.
   virtual void DidInsertCSS() {}
 
   // A different node in the page got focused.
   virtual void FocusedNodeChanged() {}
 };
 
 #endif  // CHROME_BROWSER_RENDERER_HOST_RENDER_VIEW_HOST_DELEGATE_H_