MSE: Start letting SourceBuffer begin to do initialization segment received algorithm

Source/modules/mediasource/SourceBufferList.cpp

Index: Source/modules/mediasource/SourceBufferList.cpp
diff --git a/Source/modules/mediasource/SourceBufferList.cpp b/Source/modules/mediasource/SourceBufferList.cpp
index f6be0f6c36b516af37dfe57ef9a86f9bf8e2b18f..3525830a5fc801b3eb19ba6a2703d192d25b7b61 100644
--- a/Source/modules/mediasource/SourceBufferList.cpp
+++ b/Source/modules/mediasource/SourceBufferList.cpp
@@ -57,6 +57,12 @@ void SourceBufferList::add(SourceBuffer* buffer)
     scheduleEvent(EventTypeNames::addsourcebuffer);
 }
 
+void SourceBufferList::insert(size_t position, SourceBuffer* buffer)
+{
+    m_list.insert(position, buffer);
+    scheduleEvent(EventTypeNames::addsourcebuffer);
+}
+
 void SourceBufferList::remove(SourceBuffer* buffer)
 {
     size_t index = m_list.find(buffer);