Have SourceBufferList trace all its object references.

Source/modules/mediasource/SourceBufferList.h

Index: Source/modules/mediasource/SourceBufferList.h
diff --git a/Source/modules/mediasource/SourceBufferList.h b/Source/modules/mediasource/SourceBufferList.h
index 64a5f6f7073acc4bb090aabedce7d8c38be6deaf..5c00b3ff2df7c59e6a7ddc47cf07ad45f9f4280d 100644
--- a/Source/modules/mediasource/SourceBufferList.h
+++ b/Source/modules/mediasource/SourceBufferList.h
@@ -33,7 +33,6 @@
 
 #include "modules/EventTargetModules.h"
 #include "platform/heap/Handle.h"
-#include "wtf/Vector.h"
 
 namespace blink {
 
@@ -72,10 +71,10 @@ private:
 
     void scheduleEvent(const AtomicString&);
 
-    ExecutionContext* m_executionContext;
-    GenericEventQueue* m_asyncEventQueue;
+    RawPtrWillBeMember<ExecutionContext> m_executionContext;
+    RawPtrWillBeMember<GenericEventQueue> m_asyncEventQueue;
 
-    HeapVector<Member<SourceBuffer> > m_list;
+    HeapVector<Member<SourceBuffer>> m_list;
 };
 
 } // namespace blink