Add observer interface to PrerenderContents.

This CL adds a simple Observer interface to PrerenderContents, and makes the PrerenderTracker an observer. The PrerenderHandle will become an observer in a soon to be uploaded CL....

The most interesting change here is that the prerender_unittest is now testing with a tracker, so it has to pass in reasonable route IDs.

R=mmenke@chromium.org
BUG=None


Review URL: https://chromiumcodereview.appspot.com/11348357

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@171995 0039d316-1c4b-4281-b951-d872f2087c98
9 files changed