cps: Use BuiltinOperator.IsNumber for 'is num'

pkg/compiler/lib/src/cps_ir/type_propagation.dart

Index: pkg/compiler/lib/src/cps_ir/type_propagation.dart
diff --git a/pkg/compiler/lib/src/cps_ir/type_propagation.dart b/pkg/compiler/lib/src/cps_ir/type_propagation.dart
index d93f05154e3baff2b274c9ff9ab737d14b9abd1f..43f912cf44df88d5f1bdc3154ab8c55ebcf2a2f9 100644
--- a/pkg/compiler/lib/src/cps_ir/type_propagation.dart
+++ b/pkg/compiler/lib/src/cps_ir/type_propagation.dart
@@ -1784,6 +1784,13 @@ class TransformingVisitor extends LeafVisitor {
           <Primitive>[prim, prim, prim],
           node.sourceInformation);
     }
+    if (node.type == dartTypes.coreTypes.numType ||
+        node.type == dartTypes.coreTypes.doubleType) {
+      return new ApplyBuiltinOperator(
+          BuiltinOperator.IsNumber,
+          <Primitive>[prim],
+          node.sourceInformation);
+    }
     return null;
   }