Do not show shelf or top chrome hints while in Ash immersive mode

Introduced a new Material Design controller called IsImmersiveModeMaterial,
which controls the default behavior of ash immersive mode. By default, the
immersive mode hints on top chrome and on shelf are hidden. The hints are
showing when the flag ash-md is set to disabled.

TEST=Shelf_layout_manager_unittests, immersive_mode_controller_ash_unittests

BUG=641951, 623432

Review-Url: https://codereview.chromium.org/2326703002
Cr-Commit-Position: refs/heads/master@{#417461}
8 files changed