DevTools: duplicate permission bubbles are seen on every docking of devtools as seperate window.
DevTools: duplicate permission bubbles are seen on every docking of devtools as seperate window.

BUG=560140

Review URL: https://codereview.chromium.org/1487633004

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#362217}

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