Cleanup: remove unneeded inlcudes and make shared constants actually shared.

BUG=None.

Review URL: https://codereview.chromium.org/180863002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@253571 0039d316-1c4b-4281-b951-d872f2087c98
Delete some VariationsService histograms that are not useful.

BUG=none

Review URL: https://codereview.chromium.org/179983004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@253572 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 253572
Delete newly unused SnapSizer class. I missed deleting the files in https://codereview.chromium.org/178573002/

BUG=343276
TEST=None
TBR=oshima

Review URL: https://codereview.chromium.org/181673002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@253573 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 253573
Documentation for settings override API

BUG=267510
R=kalman@chromium.org, mkearney@chromium.org

Review URL: https://codereview.chromium.org/181963002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@253575 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 253575