Fixes bug in mips left shift.

tests/language/load_to_load_forwarding_vm_test.dart

 // Copyright (c) 2012, 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.
 // Test correctness of side effects tracking used by load to load forwarding.
 
+// VMOptions=--optimization-counter-threshold=10
+
 import "package:expect/expect.dart";
 import "dart:typed_data";
 
 class A {
   var x, y;
   A(this.x, this.y);
 }
 
 foo(a) {
   var value1 = a.x;
@@ skipping 183 matching lines @@
   testImmutableVMFields(fixed, true);
   testImmutableVMFields(growable, false);
   testImmutableVMFields(growable, false);
 
   final f64List = new Float64List(2);
   testPhiRepresentation(true, f64List);
   testPhiRepresentation(false, f64List);
 
   final obj = new X(new X(new X(null)));
 
-  for (var i = 0; i < 2000; i++) {
+  for (var i = 0; i < 20; i++) {
     Expect.listEquals([0x02010000, 0x03020100], foo(new A(0, 0)));
     Expect.listEquals([0x02010000, 0x03020100], bar(new A(0, 0), false));
     Expect.listEquals([0x04020000, 0x03020100], bar(new A(0, 0), true));
     testImmutableVMFields(fixed, true);
     testPhiRepresentation(true, f64List);
     testPhiForwarding(obj);
     testPhiForwarding2(obj);
     testPhiForwarding3();
     testPhiForwarding4();
     testEqualPhisElimination();
@@ skipping 12 matching lines @@
   for (var i = 0; i < 4000; i++) {
     testPhiConvertions(true, u32List);
     testPhiConvertions(false, u32List);
   }
 
   final escape = new List(1);
   for (var i = 0; i < 10000; i++) {
     fakeAliasing(escape);
   }
 }