Fetch API: Fix behavior when Request constructor is passed an undefined referrer

third_party/WebKit/Source/modules/fetch/RequestInit.cpp

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "modules/fetch/RequestInit.h"
 
 #include "bindings/core/v8/Dictionary.h"
 #include "bindings/core/v8/V8ArrayBuffer.h"
 #include "bindings/core/v8/V8ArrayBufferView.h"
 #include "bindings/core/v8/V8Binding.h"
@@ skipping 27 matching lines @@
       headers = Headers::create(headersVector, exceptionState);
       areAnyMembersSet = true;
     } else {
       areAnyMembersSet |=
           DictionaryHelper::get(options, "headers", headersDictionary);
     }
   }
   areAnyMembersSet |= DictionaryHelper::get(options, "mode", mode);
   areAnyMembersSet |= DictionaryHelper::get(options, "redirect", redirect);
   AtomicString referrerString;
-  bool isReferrerStringSet =
-      DictionaryHelper::get(options, "referrer", referrerString);
+  bool isReferrerStringSet = DictionaryHelper::getWithUndefinedCheck(
+      options, "referrer", referrerString);
   areAnyMembersSet |= isReferrerStringSet;
   areAnyMembersSet |= DictionaryHelper::get(options, "integrity", integrity);
   AtomicString referrerPolicyString;
   bool isReferrerPolicySet =
       DictionaryHelper::get(options, "referrerPolicy", referrerPolicyString);
   areAnyMembersSet |= isReferrerPolicySet;
 
   v8::Local<v8::Value> v8Body;
   bool isBodySet = DictionaryHelper::get(options, "body", v8Body);
   areAnyMembersSet |= isBodySet;
@@ skipping 88 matching lines @@
         AtomicString("application/x-www-form-urlencoded;charset=UTF-8");
     body = new FormDataBytesConsumer(context, formData.release());
   } else if (v8Body->IsString()) {
     contentType = "text/plain;charset=UTF-8";
     body =
         new FormDataBytesConsumer(toUSVString(isolate, v8Body, exceptionState));
   }
 }
 
 }  // namespace blink