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Previously WorkspaceManager was used for this container which resulted in various
issues when login screen window was not full screen and was supposed to be resized
only by virtual keyboard container. Otherwise panels and shelf were taken into account
even though they are stacked below the lock container.

This CL improves previous fix
https://codereview.chromium.org/231123002

Disable this layout manager with --ash-disable-lock-layout-manager

Verified that existing out-of-box/login/multi-profiles login/lock* virtual keyboard
overscroll/non-overscroll configurations work fine.

Non-overscroll lock screen configuration is updated to use the same behavior as
login in https://codereview.chromium.org/320523003

BUG=375666
TEST=LockLayoutManager.*, existing tests

Review URL: https://codereview.chromium.org/254673004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@275431 0039d316-1c4b-4281-b951-d872f2087c98