Use "unsigned" rather than "unsigned long" for C++ code interacting with WebIDL's "unsigned long".

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 d7b60caaf1b8911f45a17844b2b60de398318c48..64a5f6f7073acc4bb090aabedce7d8c38be6deaf 100644
--- a/Source/modules/mediasource/SourceBufferList.h
+++ b/Source/modules/mediasource/SourceBufferList.h
@@ -51,8 +51,8 @@ public:
     }
     virtual ~SourceBufferList();
 
-    unsigned long length() const { return m_list.size(); }
-    SourceBuffer* item(unsigned long index) const { return (index < m_list.size()) ? m_list[index].get() : 0; }
+    unsigned length() const { return m_list.size(); }
+    SourceBuffer* item(unsigned index) const { return (index < m_list.size()) ? m_list[index].get() : 0; }
 
     void add(SourceBuffer*);
     void insert(size_t position, SourceBuffer*);