Revert "dart2js cps: Change type tests to null tests when applicable."

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 b8fa9184826c37286420b1138db3e8ff970ecc6c..0bcd7a9d05229f57950b57ce676c14aa10148502 100644
--- a/pkg/compiler/lib/src/cps_ir/type_propagation.dart
+++ b/pkg/compiler/lib/src/cps_ir/type_propagation.dart
@@ -43,15 +43,12 @@ class ConstantPropagationLattice {
   final ConstantSystem constantSystem;
   final types.DartTypes dartTypes;
   final AbstractValue anything;
-  final AbstractValue nullValue;
 
   ConstantPropagationLattice(TypeMaskSystem typeSystem,
                              this.constantSystem,
                              this.dartTypes)
     : this.typeSystem = typeSystem,
-      anything = new AbstractValue.nonConstant(typeSystem.dynamicType),
-      nullValue = new AbstractValue.constantValue(
-          new NullConstantValue(), new TypeMask.empty());
+      anything = new AbstractValue.nonConstant(typeSystem.dynamicType);
 
   final AbstractValue nothing = new AbstractValue.nothing();
 
@@ -1833,23 +1830,6 @@ class TransformingVisitor extends LeafVisitor {
           <Primitive>[prim],
           node.sourceInformation);
     }
-    AbstractBool isNullableSubtype =
-        lattice.isSubtypeOf(value, node.dartType, allowNull: true);
-    AbstractBool isNullPassingTest =
-        lattice.isSubtypeOf(lattice.nullValue, node.dartType);
-    if (isNullableSubtype == AbstractBool.True &&
-        isNullPassingTest == AbstractBool.False) {
-      // Null is the only value not satisfying the type test.
-      // Replace the type test with a null-check.
-      // This has lower priority than the 'typeof'-based tests because
-      // 'typeof' expressions might give the VM some more useful information.
-      Primitive nullConst = makeConstantPrimitive(new NullConstantValue());
-      insertLetPrim(node.parent, nullConst);
-      return new ApplyBuiltinOperator(
-          BuiltinOperator.LooseNeq,
-          <Primitive>[prim, nullConst],
-          node.sourceInformation);
-    }
     return null;
   }