Bug 1404297 - Add a move constructor to SegmentedVector. r=smaug

Given that we have a SegmentedVector of nsCOMPtrs, it's probably worth
avoiding copying it.

MozReview-Commit-ID: GHyfVLrdnlQ

--HG--
extra : rebase_source : 75df805d8b2df32b76ee77b95ced625f20331744

mfbt/SegmentedVector.h

@@ -139,6 +139,11 @@ public:
       aIdealSegmentSize - sizeof(Segment) < sizeof(T));
   }
 
+  SegmentedVector(SegmentedVector&& aOther)
+    : mSegments(mozilla::Move(aOther.mSegments))
+  {
+  }
+
   ~SegmentedVector() { Clear(); }
 
   bool IsEmpty() const { return !mSegments.getFirst(); }