NOT FOR LANDING Introduce and use WebMediaSession

Source/core/loader/EmptyClients.cpp

Index: Source/core/loader/EmptyClients.cpp
diff --git a/Source/core/loader/EmptyClients.cpp b/Source/core/loader/EmptyClients.cpp
index 913b57de9c5dc7218a8f278217b7694fba8df8b7..2e2651ad30c7960dfd1a06b2ba096d832b97574e 100644
--- a/Source/core/loader/EmptyClients.cpp
+++ b/Source/core/loader/EmptyClients.cpp
@@ -39,6 +39,7 @@
 #include "public/platform/WebMediaPlayer.h"
 #include "public/platform/WebServiceWorkerProvider.h"
 #include "public/platform/WebServiceWorkerProviderClient.h"
+#include "public/platform/modules/mediasession/WebMediaSession.h"
 
 namespace blink {
 
@@ -129,6 +130,11 @@ PassOwnPtr<WebMediaPlayer> EmptyFrameLoaderClient::createWebMediaPlayer(HTMLMedi
     return nullptr;
 }
 
+PassOwnPtr<WebMediaSession> EmptyFrameLoaderClient::createWebMediaSession()
+{
+    return nullptr;
+}
+
 void EmptyTextCheckerClient::requestCheckingOfString(PassRefPtrWillBeRawPtr<TextCheckingRequest>)
 {
 }