Replace TypeMask.isEmpty by isEmptyOrNull, use isEmpty when it's really empty.

pkg/compiler/lib/src/ssa/interceptor_simplifier.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of ssa;
 
 /**
  * This phase simplifies interceptors in multiple ways:
  *
  * 1) If the interceptor is for an object whose type is known, it
@@ skipping 117 matching lines @@
     ConstantValue constant =
         new InterceptorConstantValue(constantInterceptor.thisType);
     return graph.addConstant(constant, compiler);
   }
 
   ClassElement tryComputeConstantInterceptorFromType(
       TypeMask type,
       Set<ClassElement> interceptedClasses) {
 
     if (type.isNullable) {
-      if (type.isEmpty) {
+      if (type.isNull) {
         return helpers.jsNullClass;
       }
     } else if (type.containsOnlyInt(classWorld)) {
       return helpers.jsIntClass;
     } else if (type.containsOnlyDouble(classWorld)) {
       return helpers.jsDoubleClass;
     } else if (type.containsOnlyBool(classWorld)) {
       return helpers.jsBoolClass;
     } else if (type.containsOnlyString(classWorld)) {
       return helpers.jsStringClass;
@@ skipping 253 matching lines @@
       instruction = new HInvokeDynamicMethod(
           selector, mask, inputs, node.instructionType, true);
     }
 
     HBasicBlock block = node.block;
     block.addAfter(node, instruction);
     block.rewrite(node, instruction);
     return true;
   }
 }