DevTools: pinch zoom around current cursor location while emulating touch.
DevTools: pinch zoom around current cursor location while emulating touch.

R=vsevik@chromium.org
TBR=vsevik

Review URL: https://codereview.chromium.org/54993007

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@161157 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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