Make ResourceHandlers stateless with respect to child/routing/request IDs.
This lets us transfer an existing handler chain to a new process.

BUG=238331
TEST=Follow a link that redirects to the Chrome Web Store.
R=ajwong@chromium.org, darin@chromium.org, mpcomplete@chromium.org

Review URL: https://codereview.chromium.org/23180005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@225263 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 225263