DevTools: fix crash when inspect element invoked on the root element.
DevTools: fix crash when inspect element invoked on the root element.

Review URL: http://codereview.chromium.org/131106

git-svn-id: http://src.chromium.org/svn/trunk/src@18805 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

Former-commit-id: 9c1bd25d3930d5ebac1a9e159314f343054d1f5b
meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser