DevTools: always zoom on wheel in flame chart.
DevTools: always zoom on wheel in flame chart.

NOTRY=true

Review URL: https://codereview.chromium.org/458353005

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@180091 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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