GitLab

Currently, if an extension message bubble is shown, and then it is dismissed
because it loses focus, we treat it the same as the user clicking the dismiss
button - which serves as acknowledging the extension.  We could ignore focus
loss, but this makes for very noisy, awkward bubbles.  Instead, allow the bubble
to close, but don't treat this as user acknowledgment, and show the bubble again
on next startup.

This also involves tracking the close reason for a BubbleDelegateView.

BUG=548269
TBR=finnur@chromium.org (no changes relevant from original CL)
TBR=avi@chromium.org (no changes relevant from original CL)

Review URL: https://codereview.chromium.org/1455313002

Cr-Commit-Position: refs/heads/master@{#360848}