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- Add |alertStates| as property on |TabData|, sent from C++
- Move fade in and fade out animations out from CSS to JS to allow
wrapping them within Promises, so that TabElement can reliably tell
when there are AlertIndicator elements in the DOM.
- Fix tests such that SVGs load from chrome://tab-strip instead of
chrome://test.

Screencast in attached bug.

Bug: 1004983
Change-Id: I32cb6c91169646c244070826875a8317b8c9b296
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1861124Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Commit-Queue: John Lee <johntlee@chromium.org>
Cr-Commit-Position: refs/heads/master@{#707217}