Record histograms of the cookie status of a prerender:
We record a bitmap of which of the four combinations
(send cookies, change cookies) x (main frame http request, other resource)
occur.
To determine whether a cookie presented was created as part of the prerender
or existed before, we check the cookie creation time relative to prerender
start. This may be inaccurate if the user happens to browse the same domain
while a prerender is in progress, but we will assume this is not very common.

R=asvitkine@chromium.org, davidben@chromium.org, jochen@chromium.org

Review URL: https://codereview.chromium.org/133913003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@244662 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 244662