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 4f8a3f26c139feb35a84f65b01cf1d0530e1133f..e5d85593110e857e9349d26209ea20b1be85cdff 100644
--- a/content/public/browser/web_contents.h
+++ b/content/public/browser/web_contents.h
@@ -697,7 +697,6 @@ 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.
@@ -705,6 +704,7 @@ 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;