Re-disable V8-based proxy resolving with the --single-process command line is set.

BUG=474654

Review URL: https://codereview.chromium.org/1067903003

Cr-Commit-Position: refs/heads/master@{#324087}

chrome/browser/net/proxy_service_factory.cc

@@ -104,6 +104,13 @@ net::ProxyService* ProxyServiceFactory::CreateProxyService(
   bool use_v8 = false;
 #else
   bool use_v8 = !command_line.HasSwitch(switches::kWinHttpProxyResolver);
+  // TODO(eroman): Figure out why this doesn't work in single-process mode.
+  // Should be possible now that a private isolate is used.
+  // http://crbug.com/474654
+  if (use_v8 && command_line.HasSwitch(switches::kSingleProcess)) {
+    LOG(ERROR) << "Cannot use V8 Proxy resolver in single process mode.";
+    use_v8 = false;  // Fallback to non-v8 implementation.
+  }
 #endif  // defined(OS_IOS)
 
   size_t num_pac_threads = 0u;  // Use default number of threads.