Enable (optional) blocking of webrequests in case a PAC script cannot be fetched or is invalid.

chrome/browser/net/pref_proxy_config_service.cc

Index: chrome/browser/net/pref_proxy_config_service.cc
diff --git a/chrome/browser/net/pref_proxy_config_service.cc b/chrome/browser/net/pref_proxy_config_service.cc
index 7862be9b6f8c741d9fbf1d123f6bf4815ae3e06d..f8679236375b57ed280575cce7d2e716c262fcc9 100644
--- a/chrome/browser/net/pref_proxy_config_service.cc
+++ b/chrome/browser/net/pref_proxy_config_service.cc
@@ -137,6 +137,9 @@ bool PrefProxyConfigTracker::PrefConfigToNetConfig(
         return true;
       }
       config->set_pac_url(proxy_pac_url);
+      bool pac_mandatory = false;
+      proxy_dict.GetPacMandatory(&pac_mandatory);
+      config->set_pac_mandatory(pac_mandatory);
       return true;
     }
     case ProxyPrefs::MODE_FIXED_SERVERS: {