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/client_handler_std.h

@@ -14,7 +14,9 @@ namespace client {
 // one browser per handler instance.
 class ClientHandlerStd : public ClientHandler {
  public:
-  ClientHandlerStd(Delegate* delegate, const std::string& startup_url);
+  ClientHandlerStd(Delegate* delegate,
+                   bool with_controls,
+                   const std::string& startup_url);
 
  private:
   // Include the default reference counting implementation.