Implements #2734 “New API to configure BrowserWindow title bar on Mac”

New API supported on Yosemite 10.10 and newer.

atom/common/options_switches.cc

@@ -42,6 +42,9 @@ const char kAcceptFirstMouse[] = "accept-first-mouse";
 // Whether window size should include window frame.
 const char kUseContentSize[] = "use-content-size";
 
+// The requested title bar style for the window
+const char kTitleBarStyle[] = "title-bar-style";
+
 // The WebPreferences.
 const char kWebPreferences[] = "web-preferences";