DevTools: NOOP if outline dialog is not available for the content type

Currently hitting Ctrl-Shift-O on any typescript/python/C++ file in
DevTools will result in opened bookmarks tab (at least on linux).
Almost all the time, if user is editing code in Sources Panel and hitting
Ctrl-Shift-O, he expects outline dialog to be shown.

As we are not capable of supporting all the fancy file formats yet, the patch
suggests swallowing Ctrl-Shift-O for those content types that we do not support.

R=vsevik, apavlov, pfeldman

Review URL: https://codereview.chromium.org/422023002

git-svn-id: svn://svn.chromium.org/blink/trunk@179049 bbb929c8-8fbe-4397-9dbb-9b2b20218538