Correct calculation of the `DoBrowserControlsShrinkRendererSize` bit

Update it such that it matches the bounds changes we make to the
BrowserView and in turn the BrowserView::contents_web_view_, so that
it's true only when top-chrome is fully shown.

Make sure it gets updated only:
- Once right before the layout that happens at OnBeginSliding().
- Right before the layout that happens at OnSlidingEnds().

BUG=927985
TEST=Adjusted tests.

Change-Id: I00bbc49c5ad7e1cebf607b824011b97708570bd8
Reviewed-on: https://chromium-review.googlesource.com/c/1460422
Commit-Queue: Ahmed Fakhry <afakhry@chromium.org>
Reviewed-by: David Bokan <bokan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#631440}
2 files changed