Add a menu item to content_shell to open devtools to make it more discoverable.

content/public/browser/devtools_http_handler.h

Index: content/public/browser/devtools_http_handler.h
===================================================================
--- content/public/browser/devtools_http_handler.h	(revision 150609)
+++ content/public/browser/devtools_http_handler.h	(working copy)
@@ -9,6 +9,8 @@
 
 #include "content/common/content_export.h"
 
+class GURL;
+
 namespace net {
 class StreamListenSocketFactory;
 class URLRequestContextGetter;
@@ -56,6 +58,9 @@
   // default implementation will be used.
   virtual void SetRenderViewHostBinding(RenderViewHostBinding* binding) = 0;
 
+  // Returns the URL for the address to debug |render_view_host|.
+  virtual GURL GetFrontendURL(RenderViewHost* render_view_host) = 0;
+
  protected:
   virtual ~DevToolsHttpHandler() {}
 };