Update to Chromium version 68.0.3425.0 (#557062)

Known issues:
- Surface synchronization is now enabled for OSR, see issue #2447.
- Jumbo build is broken, fixed in https://crrev.com/868717ce.

libcef/browser/net/url_request_context_getter_impl.cc

@@ -138,7 +138,7 @@ std::unique_ptr<net::ProxyResolutionService> CreateProxyResolutionService(
 
     proxy_service = network::CreateProxyResolutionServiceUsingMojoFactory(
         std::move(proxy_resolver_factory), std::move(proxy_config_service),
-        std::make_unique<net::PacFileFetcherImpl>(context),
+        net::PacFileFetcherImpl::Create(context),
         std::move(dhcp_pac_file_fetcher), context->host_resolver(), net_log,
         network_delegate);
   } else {