DevTools: [CodeMirror] fix compilation warnings
DevTools: [CodeMirror] fix compilation warnings

The patch adds a method which was just introduced to CodeMirror API into
externs.

BUG=
R=vsevik@chromium.org

Review URL: https://codereview.chromium.org/15934009

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@151744 bbb929c8-8fbe-4397-9dbb-9b2b20218538

primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs