(Merge to M-51) Revise the shelf alignment locking mechanism.

(Merge to M-51) Revise the shelf alignment locking mechanism.

Add a new SHELF_ALIGNMENT_LOCKED, not stored in user prefs.
(similar to existing SHELF_AUTO_HIDE_ALWAYS_HIDDEN behavior)

Add a new Shelf member, ShelfLockingManager.
This locks (bottom) alignment on screen lock and user addition.

Fixes a regression from https://codereview.chromium.org/1851883002

TODO: Move more state tracking (for visibility) out of LayoutManager.

BUG=603243
TEST=Locking Chrome OS moves shelf to bottom.
R=sky@chromium.org

Review URL: https://codereview.chromium.org/1877543002

Cr-Commit-Position: refs/heads/master@{#388021}
(cherry picked from commit 67a576240caed1c3783e6465d6c07998a2fc0b07)

Committed: https://chromium.googlesource.com/chromium/src/+/2b215eb84a43373060023baca3e3f375e73376e8

[msw, 2016-04-22 19:29:20]

Description was changed from

==========
(Merge to M-51) Revise the shelf alignment locking mechanism.

Add a new SHELF_ALIGNMENT_LOCKED, not stored in user prefs.
(similar to existing SHELF_AUTO_HIDE_ALWAYS_HIDDEN behavior)

Add a new Shelf member, ShelfLockingManager.
This locks (bottom) alignment on screen lock and user addition.

Fixes a regression from https://codereview.chromium.org/1851883002

TODO: Move more state tracking (for visibility) out of LayoutManager.

BUG=603243
TEST=Locking Chrome OS moves shelf to bottom.
R=sky@chromium.org

Review URL: https://codereview.chromium.org/1877543002

Cr-Commit-Position: refs/heads/master@{#388021}
(cherry picked from commit 67a576240caed1c3783e6465d6c07998a2fc0b07)
==========

to

==========
(Merge to M-51) Revise the shelf alignment locking mechanism.

Add a new SHELF_ALIGNMENT_LOCKED, not stored in user prefs.
(similar to existing SHELF_AUTO_HIDE_ALWAYS_HIDDEN behavior)

Add a new Shelf member, ShelfLockingManager.
This locks (bottom) alignment on screen lock and user addition.

Fixes a regression from https://codereview.chromium.org/1851883002

TODO: Move more state tracking (for visibility) out of LayoutManager.

BUG=603243
TEST=Locking Chrome OS moves shelf to bottom.
R=sky@chromium.org

Review URL: https://codereview.chromium.org/1877543002

Cr-Commit-Position: refs/heads/master@{#388021}
(cherry picked from commit 67a576240caed1c3783e6465d6c07998a2fc0b07)

Committed:
https://chromium.googlesource.com/chromium/src/+/2b215eb84a43373060023baca3e3...
==========

[msw, 2016-04-22 19:29:22]

Committed patchset #1 (id:1) manually as
2b215eb84a43373060023baca3e3f375e73376e8.