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

third_party/WebKit/Source/modules/credentialmanager/CredentialsContainer.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/credentialmanager/CredentialsContainer.h"
 
 #include <memory>
 #include <utility>
 #include "bindings/core/v8/Dictionary.h"
 #include "bindings/core/v8/ScriptPromise.h"
@@ skipping 72 matching lines @@
 
 class RequestCallbacks : public WebCredentialManagerClient::RequestCallbacks {
   WTF_MAKE_NONCOPYABLE(RequestCallbacks);
 
  public:
   explicit RequestCallbacks(ScriptPromiseResolver* resolver)
       : resolver_(resolver) {}
   ~RequestCallbacks() override {}
 
   void OnSuccess(std::unique_ptr<WebCredential> web_credential) override {
-    Frame* frame =
-        ToDocument(ExecutionContext::From(resolver_->GetScriptState()))
-            ->GetFrame();
+    ExecutionContext* context =
+        ExecutionContext::From(resolver_->GetScriptState());
+    if (!context)
+      return;
+    Frame* frame = ToDocument(context)->GetFrame();
     SECURITY_CHECK(!frame || frame == frame->Tree().Top());
 
     std::unique_ptr<WebCredential> credential =
         WTF::WrapUnique(web_credential.release());
     if (!credential || !frame) {
       resolver_->Resolve();
       return;
     }
 
     ASSERT(credential->IsPasswordCredential() ||
@@ skipping 100 matching lines @@
   ScriptPromise promise = resolver->Promise();
   if (!CheckBoilerplate(resolver))
     return promise;
 
   CredentialManagerClient::From(ExecutionContext::From(script_state))
       ->DispatchRequireUserMediation(new NotificationCallbacks(resolver));
   return promise;
 }
 
 }  // namespace blink