Make keyboard shortcuts work on Mac

When the renderer doesn't handle a key event, we pass it off to the main menu
to see if it can handle it.

Part of #2.

brightray/browser/default_web_contents_delegate.h

@@ -0,0 +1,21 @@
+#ifndef BRIGHTRAY_BROWSER_DEFAULT_WEB_CONTENTS_DELEGATE_H_
+#define BRIGHTRAY_BROWSER_DEFAULT_WEB_CONTENTS_DELEGATE_H_
+
+#include "content/public/browser/web_contents_delegate.h"
+
+namespace brightray {
+
+// This class provides some sane default behaviors to any content::WebContents instance (e.g.,
+// keyboard shortcut handling on Mac).
+class DefaultWebContentsDelegate : public content::WebContentsDelegate {
+public:
+  DefaultWebContentsDelegate();
+  ~DefaultWebContentsDelegate();
+
+protected:
+  virtual void HandleKeyboardEvent(content::WebContents*, const content::NativeWebKeyboardEvent&) OVERRIDE;
+};
+
+}
+
+#endif