Bug 863439 - Use BoxInputsPolicy for MUnbox.

js/src/ion/MIR.h

@@ -1914,7 +1914,7 @@ JSOpToCondition(MCompare::CompareType compareType, JSOp op)
 // Takes a typed value and checks if it is a certain type. If so, the payload
 // is unpacked and returned as that type. Otherwise, it is considered a
 // deoptimization.
-class MUnbox : public MUnaryInstruction
+class MUnbox : public MUnaryInstruction, public BoxInputsPolicy
 {
   public:
     enum Mode {
@@ -1955,6 +1955,10 @@ class MUnbox : public MUnaryInstruction
         return new MUnbox(ins, type, mode);
     }
 
+    TypePolicy *typePolicy() {
+        return this;
+    }
+
     Mode mode() const {
         return mode_;
     }