--- a/dom/media/Intervals.h
+++ b/dom/media/Intervals.h
@@ -628,16 +628,26 @@ public:
     for (const auto& interval : mIntervals) {
       if (interval.ContainsWithStrictEnd(aX)) {
         return true;
       }
     }
     return false;
   }
 
+  bool ContainsWithStrictEnd(const ElemType& aInterval) const
+  {
+    for (const auto& interval : mIntervals) {
+      if (interval.ContainsWithStrictEnd(aInterval)) {
+        return true;
+      }
+    }
+    return false;
+  }
+
   // Shift all values by aOffset.
   SelfType& Shift(const T& aOffset)
   {
     for (auto& interval : mIntervals) {
       interval.mStart = interval.mStart + aOffset;
       interval.mEnd = interval.mEnd + aOffset;
     }
     return *this;