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

chrome/test/data/extensions/api_test/proxy/pacdata/test.js

Index: chrome/test/data/extensions/api_test/proxy/pacdata/test.js
diff --git a/chrome/test/data/extensions/api_test/proxy/pacdata/test.js b/chrome/test/data/extensions/api_test/proxy/pacdata/test.js
index e5cb541a001991443312b436c316493bd77133b9..deec64d52ace948958f550960f2997ea44a1135a 100644
--- a/chrome/test/data/extensions/api_test/proxy/pacdata/test.js
+++ b/chrome/test/data/extensions/api_test/proxy/pacdata/test.js
@@ -18,7 +18,8 @@ chrome.test.runTests([
             "  if (host == 'foobar.com')\n" +
             "    return 'PROXY blackhole:80';\n" +
             "  return 'DIRECT';\n" +
-            "}"
+            "}",
+      mandatory: false
     };
     var config = {
       mode: "pac_script",