Merge BaseLayoutManager into WorkspaceLayoutManager

BUG=338906
R=pkotwicz@chromium.org

Review URL: https://codereview.chromium.org/153143003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@248784 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 248784