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 548 matching lines @@
     invalidate: "ViewportDescription",
   },
 
   {
     name: "dnsPrefetchingEnabled",
     initial: false,
     invalidate: "DNSPrefetching",
   },
 
   {
+    name: "encryptedMediaEnabled",
+    initial: true,
+  },
+
+  {
     name: "dataSaverEnabled",
     initial: false,
   },
 
   // FIXME: This is a temporary flag and should be removed
   // when squashing is ready. (crbug.com/261605)
   {
     name: "layerSquashingEnabled",
     initial: false,
   },
@@ skipping 344 matching lines @@
   },
 
   // Whether the frame is a presentation receiver and should expose
   // `navigator.presentation.receiver`.
   {
     name: "presentationReceiver",
     initial: false,
   },
 ]
 }