Work around a clang/win bug, add a .h file to gyp/gn files.

media/base/cdm_config.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 MEDIA_BASE_CDM_CONFIG_H_
 #define MEDIA_BASE_CDM_CONFIG_H_
 
 #include "media/base/media_export.h"
 
 namespace media {
 
 // The runtime configuration for new CDM instances as computed by
 // |requestMediaKeySystemAccess|. This is in some sense the Chromium-side
 // counterpart of Blink's WebMediaKeySystemConfiguration.
-struct MEDIA_EXPORT CdmConfig {
+struct CdmConfig {
   // Allow access to a distinctive identifier.
   bool allow_distinctive_identifier = false;
 
   // Allow access to persistent state.
   bool allow_persistent_state = false;
 
   // Use hardware-secure codecs. This flag is only used on Android, it should
   // always be false on other platforms.
   bool use_hw_secure_codecs = false;
 };
 
 }  // namespace media
 
 #endif  // MEDIA_BASE_CDM_CONFIG_H_