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 032ec6de3b23c869a2d1473e11a1065784b84188..3b7383be084a410be7795f307c2def72ecd93752 100644
--- a/Source/modules/mediasource/SourceBufferList.cpp
+++ b/Source/modules/mediasource/SourceBufferList.cpp
@@ -56,6 +56,12 @@ 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);