Have (new URLSearchParams(initString)) skip initial '?'.

third_party/WebKit/Source/core/dom/URLSearchParams.cpp

 // Copyright 2015 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 "core/dom/URLSearchParams.h"
 
 #include "core/dom/DOMURL.h"
 #include "platform/network/FormDataEncoder.h"
 #include "platform/weborigin/KURL.h"
 #include "wtf/text/StringBuilder.h"
@@ skipping 20 matching lines @@
 
 private:
     Vector<std::pair<String, String>> m_params;
     size_t m_current;
 };
 
 } // namespace
 
 URLSearchParams* URLSearchParams::create(const URLSearchParamsInit& init)
 {
-    if (init.isUSVString())
-        return new URLSearchParams(init.getAsUSVString());
+    if (init.isUSVString()) {
+        const String& queryString = init.getAsUSVString();
+        if (queryString.startsWith('?'))
+            return new URLSearchParams(queryString.substring(1));
+        return new URLSearchParams(queryString);
+    }
     if (init.isURLSearchParams())
         return new URLSearchParams(init.getAsURLSearchParams());
 
     DCHECK(init.isNull());
     return new URLSearchParams(String());
 }
 
 URLSearchParams::URLSearchParams(const String& queryString, DOMURL* urlObject)
     : m_urlObject(urlObject)
 {
@@ skipping 162 matching lines @@
         FormDataEncoder::addKeyValuePairAsFormData(encodedData, param.first.utf8(), param.second.utf8(), EncodedFormData::FormURLEncoded);
     return EncodedFormData::create(encodedData.data(), encodedData.size());
 }
 
 PairIterable<String, String>::IterationSource* URLSearchParams::startIteration(ScriptState*, ExceptionState&)
 {
     return new URLSearchParamsIterationSource(m_params);
 }
 
 } // namespace blink