ui: Bubble fix
woops, when I was testing this, I hadn't noticed the mistake because
I was testing over a white background, and the shadow looks exactly
like the bubble in that case.
I had used the wrong color for the shadow color, and as a result I
didn't notice that the shadow was in the wrong spot.
I did a bit more extensive testing, if you have chrome fullscreen on the
left side, and you show the bubble on the right, it does extend to right
screen by 1 pixel. This happened before and after my change.
BUG=435910
Review URL: https://codereview.chromium.org/
792243002
Cr-Commit-Position: refs/heads/master@{#308252}