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
void LiveSyncTest::SetProxyConfig(net::URLRequestContextGetter* context_getter,
                                  const net::ProxyConfig& proxy_config) {
  base::WaitableEvent done(false, false);
  BrowserThread::PostTask(
      BrowserThread::IO,
      FROM_HERE,
      new SetProxyConfigTask(&done,
                             context_getter,
                             proxy_config));
  done.Wait();
}

void LiveSyncTest::SetProxyConfig(net::URLRequestContextGetter* context_getter,
                                  const net::ProxyConfig& proxy_config) {
  base::WaitableEvent done(false, false);
  BrowserThread::PostTask(
      BrowserThread::IO,
      FROM_HERE,
      new SetProxyConfigTask(&done,
                             context_getter,
                             proxy_config));
  done.Wait();
}
