GitLab

After user decided to switch back to FULL_WIDTH mode, Chrome should:
1. immediately position the virtual keyboard to the bottom of screen and use
the screen width as its window width
2. notify web contents about the new virtual keyboard bounds so web contents
can be scrolled correctly to avoid occlussion.

BUG=487343

Review URL: https://codereview.chromium.org/1138873003

Cr-Commit-Position: refs/heads/master@{#329690}