media: Add a web preference to enable encrypted media

third_party/WebKit/Source/core/frame/Settings.json5

 {
   // Defines properties which are available on the Settings object.
   //
   // Please think carefully before adding a new Setting.  Some questions to
   // consider are:
   // - Should this be a RuntimeEnabledFeature instead? Settings are for things
   //   which we support either values of at runtime.  Features are set at renderer
   //   process startup and are never changed. Features also tend to be set to a
   //   value based on the platform or the stability of the code in question, where
   //   as settings both codepaths need to be stable.
@@ skipping 531 matching lines @@
       name: "doHtmlPreloadScanning",
       initial: true,
     },
 
     {
       name: "pluginsEnabled",
       initial: false,
     },
 
     {
+      name: "encryptedMediaEnabled",
+      initial: true,
+    },
+
+    {
       name: "viewportEnabled",
       initial: false,
       invalidate: "ViewportDescription",
     },
     {
       name: "viewportMetaEnabled",
       initial: false,
       invalidate: "ViewportDescription",
     },
 
@@ skipping 340 matching lines @@
     },
 
     // Whether the frame is a presentation receiver and should expose
     // `navigator.presentation.receiver`.
     {
       name: "presentationReceiver",
       initial: false,
     },
   ],
 }