[MSE] Reset extra memory cost inside removedFromMediaSource()

https://bugs.webkit.org/show_bug.cgi?id=267350

Reviewed by Xabier Rodriguez-Calvar.

When the SourceBuffer is removed from a MediaSource, its TrackBuffers are cleared (and so is
its data, which can take a good amount of memory), but the SourceBuffer still accounts for
the cost of its old data, as m_extraMemoryCost isn't reset to zero.

See: #1264

This patch resets m_extraMemoryCost when the SourceBuffer is removed.

Original author: Andrzej Surdej <Andrzej_Surdej@comcast.com>

* Source/WebCore/Modules/mediasource/SourceBuffer.cpp:
(WebCore::SourceBuffer::removedFromMediaSource): Reset m_extraMemoryCost.

Canonical link: https://commits.webkit.org/272908@main

Author: eocanha

Source/WebCore/Modules/mediasource/SourceBuffer.cpp

@@ -447,6 +447,7 @@ void SourceBuffer::removedFromMediaSource()
     m_private->removedFromMediaSource();
     m_private->setIsAttached(false);
     m_source = nullptr;
+    m_extraMemoryCost = 0;
 }
 
 void SourceBuffer::seekToTime(const MediaTime& time)