Add attribute event listeners to visualViewport

These were previously available but removed in r407955. In the mean time
they made their way into the visualViewport draft spec:

But we forgot to actually re-add them. This patch adds them back in.

Bug: 760916
Change-Id: Ib2dc3dbd21d648d9118bbb88e61bba7b65369688
Reviewed-by: Dave Tapuska <>
Reviewed-by: Kent Tamura <>
Commit-Queue: David Bokan <>
Cr-Commit-Position: refs/heads/master@{#501855}
13 files changed