Simplify use of ContentDecryptionModuleResult with promises

Source/modules/encryptedmedia/SimpleContentDecryptionModuleResultPromise.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 SimpleContentDecryptionModuleResultPromise_h
+#define SimpleContentDecryptionModuleResultPromise_h
+
+#include "modules/encryptedmedia/ContentDecryptionModuleResultPromise.h"
+
+namespace blink {
+
+// This class creates a simple ContentDecryptionModuleResultPromise where the
+// implementation of complete() will resolve the promise with void. All other
+// complete() methods are not expected to be called (and will reject the
+// promise).
+class SimpleContentDecryptionModuleResultPromise : public ContentDecryptionModuleResultPromise {
+public:
+    explicit SimpleContentDecryptionModuleResultPromise(ScriptState*);
+    virtual ~SimpleContentDecryptionModuleResultPromise();
+
+    // ContentDecryptionModuleResultPromise implementation.
+    virtual void complete() override;
+};
+
+} // namespace blink
+
+#endif // SimpleContentDecryptionModuleResultPromise_h