Setting HTMLMediaElement.controller does not properly remove the 'mediagroup' content attribute

LayoutTests/media/media-controller-expected.txt

Index: LayoutTests/media/media-controller-expected.txt
diff --git a/LayoutTests/media/media-controller-expected.txt b/LayoutTests/media/media-controller-expected.txt
index 72dc25e758359783d13715e90ff57be1c320781d..55f241052635696967e38eef2c180ad3f8658abd 100644
--- a/LayoutTests/media/media-controller-expected.txt
+++ b/LayoutTests/media/media-controller-expected.txt
@@ -18,7 +18,7 @@ RUN(video.controller = controller)
 EXPECTED (video.controller == '[object MediaController]') OK
 
 Test assigning the wrong type to the controller attribute of a media element:
-TEST(video.controller = 42) THROWS("TypeError: Value is not of type MediaController") OK
+TEST(video.controller = 42) THROWS("TypeError: Failed to set the 'controller' property on 'HTMLMediaElement': The provided value is not of type 'MediaController'.") OK
 EXPECTED (video.controller == '[object MediaController]') OK
 
 Test assigning a null controller to a media element:
@@ -29,5 +29,23 @@ Test that two media elements with the same mediaGroup have the same controller:
 RUN(video.mediaGroup = 'group')
 RUN(video2.mediaGroup = 'group')
 EXPECTED (video.controller === video2.controller == 'true') OK
+
+Test that setting the controller clears the mediaGroup:
+EXPECTED (video.mediaGroup == 'group') OK
+RUN(video.controller = null)
+EXPECTED (video.controller == 'null') OK
+EXPECTED (video.hasAttribute('mediaGroup') == 'false') OK
+EXPECTED (video.mediaGroup == '') OK
+RUN(video.mediaGroup = 'group')
+EXPECTED (video.mediaGroup == 'group') OK
+RUN(video.controller = controller)
+EXPECTED (video.controller == '[object MediaController]') OK
+EXPECTED (video.hasAttribute('mediaGroup') == 'false') OK
+EXPECTED (video.mediaGroup == '') OK
+
+Test that setting the controller to undefined is treated as null:
+EXPECTED (video.controller != 'null') OK
+RUN(video.controller = undefined)
+EXPECTED (video.controller == 'null') OK
 END OF TEST