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

chrome/common/chrome_switches.cc

Index: chrome/common/chrome_switches.cc
===================================================================
--- chrome/common/chrome_switches.cc	(revision 150609)
+++ chrome/common/chrome_switches.cc	(working copy)
@@ -1134,6 +1134,9 @@
 // Uses custom front-end URL for the remote debugging.
 const char kRemoteDebuggingFrontend[]       = "remote-debugging-frontend";
 
+// Enables remote debug over HTTP on the specified port.
+const char kRemoteDebuggingPort[]           = "remote-debugging-port";
+
 // Enables print preview in the renderer. This flag is generated internally by
 // Chrome and does nothing when directly passed to the browser.
 const char kRendererPrintPreview[]          = "renderer-print-preview";