chrome: Add ability to handle chrome menu/keyboard commands (fixes issue #3280)

This change adds a CefCommandHandler::OnChromeCommand callback for optionally
handling Chrome commands triggered via menus or keyboard shortcuts. Supported
command IDs are listed in a new cef_command_ids.h header file.

To test: Run `cefclient --enable-chrome-runtime --hide-controls`. Most commands
will blocked and removed from context menus.

tests/cefclient/browser/browser_window_std_gtk.h

@@ -17,7 +17,9 @@ class BrowserWindowStdGtk : public BrowserWindow {
  public:
   // Constructor may be called on any thread.
   // |delegate| must outlive this object.
-  BrowserWindowStdGtk(Delegate* delegate, const std::string& startup_url);
+  BrowserWindowStdGtk(Delegate* delegate,
+                      bool with_controls,
+                      const std::string& startup_url);
 
   // Called from RootWindowGtk::CreateRootWindow before CreateBrowser.
   void set_xdisplay(XDisplay* xdisplay);