Use HighResNow whenever possible on Windows.

This has been enabled on Canary channel for sometime now and seems to be
safe there. We also now have data from stable channel showing there are
no unexpectedly buggy CPUs out there. This should be safe to turn on for
all users with adequate CPUs, which is the majority of them.

BUG=158234

Review URL: https://codereview.chromium.org/41953002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@230968 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 230968
Remove hacks added to workaround a system salt issue for M31

In crrev.com/228189, we had to add horrible hacks to workaround an urgent
P1 issue, which needed to be merged to M31 branch immediately.

The hacks are no longer necesssary, as the system salt is obtained
before DeviceOAuth2TokenService is created. See crbug.com/309959
for details.

BUG=306547
TEST=see the bug comment #9
R=hashimoto@chromium.org

Review URL: https://codereview.chromium.org/43203002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@230969 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 230969