media: Add Feature to control External Clear Key key system support

chrome/renderer/media/chrome_key_systems.cc

 // Copyright 2013 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 "chrome/renderer/media/chrome_key_systems.h"
 
 #include <stddef.h>
 
 #include <string>
 #include <vector>
 
 #include "base/logging.h"
 #include "base/strings/string16.h"
 #include "base/strings/string_split.h"
 #include "base/strings/utf_string_conversions.h"
 #include "build/build_config.h"
 #include "chrome/common/render_messages.h"
 #include "components/cdm/renderer/widevine_key_system_properties.h"
 #include "content/public/renderer/render_thread.h"
 #include "media/base/eme_constants.h"
 #include "media/base/key_system_properties.h"
 
 #if defined(OS_ANDROID)
 #include "components/cdm/renderer/android_key_systems.h"
 #endif
 
+#if defined(ENABLE_PEPPER_CDMS)
+#include "base/feature_list.h"
+#include "media/base/media_switches.h"
+#endif
+
 #include "widevine_cdm_version.h" // In SHARED_INTERMEDIATE_DIR.
 
 // The following must be after widevine_cdm_version.h.
 
 #if defined(WIDEVINE_CDM_AVAILABLE) && defined(WIDEVINE_CDM_MIN_GLIBC_VERSION)
 #include <gnu/libc-version.h>
 #include "base/version.h"
 #endif
 
 using media::KeySystemProperties;
@@ skipping 235 matching lines @@
       media::EmeFeatureSupport::REQUESTABLE,      // Persistent state.
       media::EmeFeatureSupport::NOT_SUPPORTED));  // Distinctive identifier.
 #endif  // defined(OS_CHROMEOS)
 }
 #endif  // defined(WIDEVINE_CDM_AVAILABLE)
 #endif  // defined(ENABLE_PEPPER_CDMS)
 
 void AddChromeKeySystems(
     std::vector<std::unique_ptr<KeySystemProperties>>* key_systems_properties) {
 #if defined(ENABLE_PEPPER_CDMS)
-  AddExternalClearKey(key_systems_properties);
+  if (base::FeatureList::IsEnabled(media::kExternalClearKeyForTesting))
+    AddExternalClearKey(key_systems_properties);
 
 #if defined(WIDEVINE_CDM_AVAILABLE)
   AddPepperBasedWidevine(key_systems_properties);
 #endif  // defined(WIDEVINE_CDM_AVAILABLE)
 
 #endif  // defined(ENABLE_PEPPER_CDMS)
 
 #if defined(OS_ANDROID)
   cdm::AddAndroidWidevine(key_systems_properties);
 #endif  // defined(OS_ANDROID)
 }