Bug 1297580: P1. Remove broken optimisation in IntervalSet. r=gerald

Interval.LeftOf would always return true if the length of the interval
is less than the fuzzing value.

MozReview-Commit-ID: L9uyZjQXnGA

--HG--
extra : rebase_source : af14038da603b928c7a4942f1b37f031908e61bb

dom/media/Intervals.h

@@ -574,10 +574,6 @@ public:
 
   bool Contains(const ElemType& aInterval) const {
     for (const auto& interval : mIntervals) {
-      if (aInterval.LeftOf(interval)) {
-        // Will never succeed.
-        return false;
-      }
       if (interval.Contains(aInterval)) {
         return true;
       }