Use URLFetcher::Create instead of new in http_bridge.cc.

 This change modified http_bridge so that it uses a factory to construct
the URLFetcher. Moreover, it modified sync_backend_host_unittest.cc to
use an URLFetcher factory which will prevent access to www.example.com during
the test.

BUG=none
TEST=sync_backend_host_unittest.cc

Review URL: http://codereview.chromium.org/7053011

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@87227 0039d316-1c4b-4281-b951-d872f2087c98
TestURLFetcher::TestURLFetcher(int id,
                               const GURL& url,
                               URLFetcher::RequestType request_type,
                               URLFetcher::Delegate* d)
    : URLFetcher(url, request_type, d),
      id_(id),
      original_url_(url),
      did_receive_last_chunk_(false) {
}

TestURLFetcher::TestURLFetcher(int id,
                               const GURL& url,
                               URLFetcher::RequestType request_type,
                               URLFetcher::Delegate* d)
    : URLFetcher(url, request_type, d),
      id_(id),
      original_url_(url),
      did_receive_last_chunk_(false) {
}
