Use a framed window on Mac.

Since Mac does not support transparency, having a window with no title bar is inconvenient because it can't be dragged aside to access other windows. This CL adds a standard window frame on Mac.

BUG=b/19370387

Review URL: https://codereview.chromium.org/952823003

Cr-Commit-Position: refs/heads/master@{#318128}

remoting/webapp/app_remoting/js/ar_background.js

@@ -28,7 +28,7 @@ function createWindow(opt_launchData) {
 
   var windowAttributes = {
     resizable: false,
-    frame: 'none',
+    frame: remoting.platformIsMac() ? 'chrome' : 'none',
     bounds: {
       width: typed_screen.availWidth,
       height: typed_screen.availHeight