Move ScreenMagnifierPolicyHandler tests to chrome/browser/chromeos/...

This facilitates the refactoring of chrome/browser/policy into a layered
component.

Note that the tests have been refactored to avoid reliance on the
ConfigurationPolicyPrefStore.

BUG=271392
R=pneubeck@chromium.org

Review URL: https://codereview.chromium.org/38943006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@230974 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 230974
Telemetry: add memory pressure test for Chrome OS

This test opens a large number of tabs until a tab discard or kill event
occurs.

BUG=chromium:309683
TEST=ran the test

Review URL: https://codereview.chromium.org/38283002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@230975 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 230975