Web Inspector: fix SourceFrame.js compilation warning
https://bugs.webkit.org/show_bug.cgi?id=112804

Patch by Andrey Lushnikov <lushnikov@chromium.org> on 2013-03-20
Reviewed by Yury Semikhatsky.

No new tests: no change in behavior.

- Explicitly parse lineNumber from object property name.
- Add type annotations to ensure addMessageToSource is monomorphic.

* inspector/front-end/SourceFrame.js:
(WebInspector.SourceFrame.prototype.clearMessages):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@146345 268f45cc-cd09-0410-ab3c-d52691b4dbfc