Change type of EncodedVideoChunkInit.data to AllowSharedBufferSource

Addressing: #788

Author: Djuffin

index.src.html

@@ -2524,7 +2524,7 @@
   required EncodedAudioChunkType type;
   [EnforceRange] required long long timestamp;    // microseconds
   [EnforceRange] unsigned long long duration;     // microseconds
-  required BufferSource data;
+  required AllowSharedBufferSource data;
   sequence<ArrayBuffer> transfer = [];
 };