Don't increment lazy keep alive count on redirects.

Don't increment lazy keep alive count on redirects.

The ChromeExtensionNetworkDelegate::OnBeforeURLRequest is called for new
requests as well as for redirects. This results in the lazy keep alive
count in extensions to be incremented several times if there is a redirect
but then it is decremented only ones when the request finishes. In consequence
the lazy extension page never shuts down because the count never reaches
zero.

With this commit requests that have been redirected at least once are
ignored when incrementing the keep alive count.

BUG=175279

Review URL: https://codereview.chromium.org/464933002

Cr-Commit-Position: refs/heads/master@{#289260}
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@289260 0039d316-1c4b-4281-b951-d872f2087c98