Change initDataType and sessionType to be enums

public/platform/WebEncryptedMediaTypes.h

+// 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.
+
+#ifndef WebEncryptedMediaTypes_h
+#define WebEncryptedMediaTypes_h
+
+namespace blink {
+
+// From https://w3c.github.io/encrypted-media/initdata-format-registry.html#registry
+enum class WebEncryptedMediaInitDataType {
+    Unknown,
+    Cenc,
+    Keyids,
+    Webm,
+};
+
+// From https://w3c.github.io/encrypted-media/#idl-def-MediaKeySessionType
+enum class WebEncryptedMediaSessionType {
+    Unknown,
+    Temporary,
+    PersistentLicense,
+    PersistentReleaseMessage,
+};
+
+} // namespace blink
+
+#endif // WebEncryptedMediaTypes_h