[Blink>Media] Add Chrome feature for disabling autoplay unmuted in WebAPK

chrome/common/chrome_features.h

 // Copyright 2016 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.
 
 // This file defines all the public base::FeatureList features for the chrome
 // module.
 
 #ifndef CHROME_COMMON_CHROME_FEATURES_H_
 #define CHROME_COMMON_CHROME_FEATURES_H_
 
 #include "base/feature_list.h"
 #include "extensions/features/features.h"
 #include "ppapi/features/features.h"
 #include "printing/features/features.h"
 
 namespace features {
 
 // All features in alphabetical order. The features should be documented
 // alongside the definition of their values in the .cc file.
 
+#if defined(OS_ANDROID)
+extern const base::Feature kAllowAutoplayUnmutedInWebappManifestScope;
+#endif  // defined(OS_ANDROID)
+
 #if defined(OS_MACOSX)
 extern const base::Feature kAppleScriptExecuteJavaScript;
 #endif  // defined(OS_MACOSX)
 
 #if defined(OS_CHROMEOS)
 extern const base::Feature kArcMemoryManagement;
 #endif  // defined(OS_CHROMEOS)
 
 extern const base::Feature kAssetDownloadSuggestionsFeature;
 
@@ skipping 125 matching lines @@
 
 extern const base::Feature kCrosCompUpdates;
 #endif  // defined(OS_CHROMEOS)
 
 // DON'T ADD RANDOM STUFF HERE. Put it in the main section above in
 // alphabetical order, or in one of the ifdefs (also in order in each section).
 
 }  // namespace features
 
 #endif  // CHROME_COMMON_CHROME_FEATURES_H_