[DevTools] Fix port forwarding indication not updating properly on re-enabling.
[DevTools] Fix port forwarding indication not updating properly on re-enabling.

BUG=512150

Review URL: https://codereview.chromium.org/1354573003

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#349591}

axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk