Add a nullptr check in blink::RequestCallbacks::onSuccess to fix crash.

third_party/WebKit/Source/modules/credentialmanager/CredentialsContainer.h

 // 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.
 
 #ifndef CredentialsContainer_h
 #define CredentialsContainer_h
 
+#include "modules/ModulesExport.h"
 #include "platform/bindings/ScriptWrappable.h"
 #include "platform/heap/Handle.h"
 
 namespace blink {
 
 class Credential;
 class CredentialRequestOptions;
 class ScriptPromise;
 class ScriptState;
 
-class CredentialsContainer final
+class MODULES_EXPORT CredentialsContainer final
     : public GarbageCollected<CredentialsContainer>,
       public ScriptWrappable {
   DEFINE_WRAPPERTYPEINFO();
 
  public:
   static CredentialsContainer* Create();
 
   // CredentialsContainer.h
   ScriptPromise get(ScriptState*, const CredentialRequestOptions&);
   ScriptPromise store(ScriptState*, Credential* = 0);
   ScriptPromise requireUserMediation(ScriptState*);
 
   DEFINE_INLINE_VIRTUAL_TRACE() {}
 
  private:
   CredentialsContainer();
 };
 
 }  // namespace blink
 
 #endif  // CredentialsContainer_h