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

content/shell/shell_devtools_delegate.h

Index: content/shell/shell_devtools_delegate.h
===================================================================
--- content/shell/shell_devtools_delegate.h	(revision 150609)
+++ content/shell/shell_devtools_delegate.h	(working copy)
@@ -21,7 +21,7 @@
 
 class ShellDevToolsDelegate : public DevToolsHttpHandlerDelegate {
  public:
-  ShellDevToolsDelegate(int port, net::URLRequestContextGetter* context_getter);
+  explicit ShellDevToolsDelegate(net::URLRequestContextGetter* context_getter);
   virtual ~ShellDevToolsDelegate();
 
   // Stops http server.
@@ -32,6 +32,10 @@
   virtual bool BundlesFrontendResources() OVERRIDE;
   virtual std::string GetFrontendResourcesBaseURL() OVERRIDE;
 
+  DevToolsHttpHandler* devtools_http_handler() {
+    return devtools_http_handler_;
+  }
+
  private:
   net::URLRequestContextGetter* context_getter_;
   DevToolsHttpHandler* devtools_http_handler_;