Make MediaSession a runtime-enabled feature on Desktop.

content/public/browser/web_contents.h

Index: content/public/browser/web_contents.h
diff --git a/content/public/browser/web_contents.h b/content/public/browser/web_contents.h
index c1babd642ef95dc6e0bc2975edb4e8ac6f310595..d451653d41c6889f6cbacb2e31fcb4f425b782eb 100644
--- a/content/public/browser/web_contents.h
+++ b/content/public/browser/web_contents.h
@@ -696,7 +696,6 @@ class WebContents : public PageNavigator,
   // as soon as they are ready.
   virtual void ResumeLoadingCreatedWebContents() = 0;
 
-#if defined(OS_ANDROID)
   // Requests to resume the current media session.
   virtual void ResumeMediaSession() = 0;
   // Requests to suspend the current media session.
@@ -704,6 +703,7 @@ class WebContents : public PageNavigator,
   // Requests to stop the current media session.
   virtual void StopMediaSession() = 0;
 
+#if defined(OS_ANDROID)
   CONTENT_EXPORT static WebContents* FromJavaWebContents(
       jobject jweb_contents_android);
   virtual base::android::ScopedJavaLocalRef<jobject> GetJavaWebContents() = 0;