dart2js cps: Add instruction for bounds checks.

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

Index: pkg/compiler/lib/src/cps_ir/cps_fragment.dart
diff --git a/pkg/compiler/lib/src/cps_ir/cps_fragment.dart b/pkg/compiler/lib/src/cps_ir/cps_fragment.dart
index ada5d1a44a637b49ca7c1d68d1f15b192e437c35..5d56560bed9ac0c9b8b3183ad528a8376c401374 100644
--- a/pkg/compiler/lib/src/cps_ir/cps_fragment.dart
+++ b/pkg/compiler/lib/src/cps_ir/cps_fragment.dart
@@ -104,6 +104,7 @@ class CpsFragment {
 
   Primitive makeZero() => makeConstant(new IntConstantValue(0));
   Primitive makeOne() => makeConstant(new IntConstantValue(1));
+  Primitive makeMinusOne() => makeConstant(new IntConstantValue(-1));
   Primitive makeNull() => makeConstant(new NullConstantValue());
   Primitive makeTrue() => makeConstant(new TrueConstantValue());
   Primitive makeFalse() => makeConstant(new FalseConstantValue());
@@ -113,6 +114,10 @@ class CpsFragment {
     return letPrim(new ApplyBuiltinOperator(op, args, sourceInformation));
   }
 
+  Primitive refine(Primitive value, TypeMask type) {
+    return letPrim(new Refinement(value, type));
+  }
+
   Primitive invokeBuiltin(BuiltinMethod method,
                           Primitive receiver,
                           List<Primitive> arguments,