Move ProxyConfigService construction onto the IO thread.

chrome/browser/net/pref_proxy_config_tracker_impl.cc

Index: chrome/browser/net/pref_proxy_config_tracker_impl.cc
diff --git a/chrome/browser/net/pref_proxy_config_tracker_impl.cc b/chrome/browser/net/pref_proxy_config_tracker_impl.cc
index 6b4c30f35a42b13a52b695ae886cc6d716cbd3b2..b9213f2bc156b65fd693a38d370c9796154900bf 100644
--- a/chrome/browser/net/pref_proxy_config_tracker_impl.cc
+++ b/chrome/browser/net/pref_proxy_config_tracker_impl.cc
@@ -70,6 +70,11 @@ void ChromeProxyConfigService::OnLazyPoll() {
     base_service_->OnLazyPoll();
 }
 
+void ChromeProxyConfigService::StartTearDown() {
+  if (base_service_.get())
+    base_service_->StartTearDown();
+}
+
 void ChromeProxyConfigService::UpdateProxyConfig(
     ProxyPrefs::ConfigState config_state,
     const net::ProxyConfig& config) {
@@ -109,8 +114,10 @@ void ChromeProxyConfigService::OnProxyConfigChanged(
   if (!PrefProxyConfigTrackerImpl::PrefPrecedes(pref_config_state_)) {
     net::ProxyConfig actual_config;
     availability = GetLatestProxyConfig(&actual_config);
-    FOR_EACH_OBSERVER(net::ProxyConfigService::Observer, observers_,
-                      OnProxyConfigChanged(actual_config, availability));
+    // Don't send out notification if we don't really have a configuration yet.
+    if (availability != net::ProxyConfigService::CONFIG_PENDING)
+      FOR_EACH_OBSERVER(net::ProxyConfigService::Observer, observers_,
+                        OnProxyConfigChanged(actual_config, availability));
   }
 }