DevTools: [Console] fix console context menu handler
DevTools: [Console] fix console context menu handler

A fix to exception which was risen on right-click over console message.
This is a bug caused by r172651.

NOTRY=true

Review URL: https://codereview.chromium.org/256913003

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@172702 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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