Added the Prerender.ModPagespeedHeader.* histograms to histograms.xml. 
Extended the data extraction to also handle X-Page-Speed headers.

(dup of 20832003 which I can't commit with my personal email account)

BUG=267695

Review URL: https://codereview.chromium.org/26279004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@227685 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 227685
Disable FastShutdown test on all Macs

This doesn't need to be scoped to just Mac 64-bit.  This fails on the
Blink canaries 100% of the time.

R=ben@chromium.org
BUG=302156

Review URL: https://codereview.chromium.org/26546003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@227686 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 227686