Fix style issues of RenderThemeChromiumMac.mm.

Also, remove unused function searchMenuTemplate().
This is a follow-up of Blink r182445.

BUG=

Review URL: https://codereview.chromium.org/599713002

git-svn-id: svn://svn.chromium.org/blink/trunk@182547 bbb929c8-8fbe-4397-9dbb-9b2b20218538