fix: Fix missing override in MetaSegmentIndex

Methods on MetaSegmentIndex which should not be called directly should
be overridden from the base class.  Recently, a new method was added,
but not overridden in the subclass.  This adds an appropriate stub.

This omission had no effect on the player at runtime as far as we can
tell.

Change-Id: I3402aafdd2643f311944ff0497ad3a1c06db8175

lib/media/segment_index.js

@@ -690,7 +690,6 @@ shaka.media.MetaSegmentIndex = class extends shaka.media.SegmentIndex {
         false, 'merge() should not be used in MetaSegmentIndex!');
   }
 
-
   /**
    * @override
    * @export
@@ -702,6 +701,17 @@ shaka.media.MetaSegmentIndex = class extends shaka.media.SegmentIndex {
         false, 'evict() should not be used in MetaSegmentIndex!');
   }
 
+  /**
+   * @override
+   * @export
+   */
+  mergeAndEvict(references, windowStart) {
+    // mergeAndEvict() is only used internally by the DASH and HLS parser on
+    // SegmentIndexes, but never on MetaSegmentIndex.
+    goog.asserts.assert(
+        false, 'mergeAndEvict() should not be used in MetaSegmentIndex!');
+  }
+
   /**
    * @override
    * @export