Adjust page mobile-like behavior in tablet mode

This prevents using the mobile-viewport and the
Android-style scrollbars for pages in tablet mode.
This gives a better UX on tablets and prevents
unexpected page layout changes when switching to
tablet mode.

BUG=831473
TEST=Manually by visiting old.reddit.com/r/chromeos
     and switching to tablet mode. Page layout should
     not change to the mobile one, and ChromeOS
     scrollbars should remain in use.
     Also modified modified browser_tests.

Change-Id: Id858c03d37515f48b0f3515f099853999e3aafdd
Reviewed-on: https://chromium-review.googlesource.com/1139075
Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
Commit-Queue: Ahmed Fakhry <afakhry@chromium.org>
Cr-Commit-Position: refs/heads/master@{#575732}
2 files changed