DevTools: Added tooltip for "Run snippet" button.
DevTools: Added tooltip for "Run snippet" button.

BUG=237760
R=apavlov@chromium.org

Review URL: https://codereview.chromium.org/14885007

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@149727 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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