Optimize num::~/, num::>> and num::<< for some cases.

tests/compiler/dart2js/mock_compiler.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.
 
 library mock_compiler;
 
 import "package:expect/expect.dart";
 import 'dart:async';
 import 'dart:collection';
 
@@ skipping 113 matching lines @@
     operator+(other) => this;
   }
   class JSPositiveInt extends JSInt {}
   class JSUInt32 extends JSPositiveInt {}
   class JSUInt31 extends JSUInt32 {}
   class JSNumber extends Interceptor implements num {
     // All these methods return a number to please type inferencing.
     operator-() => (this is JSInt) ? 42 : 42.2;
     operator +(other) => (this is JSInt) ? 42 : 42.2;
     operator -(other) => (this is JSInt) ? 42 : 42.2;
-    operator ~/(other) => 42;
+    operator ~/(other) => _tdivFast(other);
     operator /(other) => (this is JSInt) ? 42 : 42.2;
     operator *(other) => (this is JSInt) ? 42 : 42.2;
     operator %(other) => (this is JSInt) ? 42 : 42.2;
-    operator <<(other) => 42;
-    operator >>(other) => 42;
+    operator <<(other) => _shlPositive(other);
+    operator >>(other) {
+      return _shrBothPositive(other) + _shrReceiverPositive(other) +
+        _shrOtherPositive(other);
+    }
     operator |(other) => 42;
     operator &(other) => 42;
     operator ^(other) => 42;
 
     operator >(other) => true;
     operator >=(other) => true;
     operator <(other) => true;
     operator <=(other) => true;
     operator ==(other) => true;
     get hashCode => throw "JSNumber.hashCode not implemented.";
 
+    _tdivFast(other) => 42;
+    _shlPositive(other) => 42;
+    _shrBothPositive(other) => 42;
+    _shrReceiverPositive(other) => 42;
+    _shrOtherPositive(other) => 42;
+
     abs() => (this is JSInt) ? 42 : 42.2;
     remainder(other) => (this is JSInt) ? 42 : 42.2;
     truncate() => 42;
   }
   class JSInt extends JSNumber implements int {
   }
   class JSDouble extends JSNumber implements double {
   }
   class JSNull extends Interceptor {
     bool operator==(other) => identical(null, other);
@@ skipping 388 matching lines @@
     } else {
       sourceFile = compiler.sourceFiles[uri.toString()];
     }
     if (sourceFile != null && begin != null && end != null) {
       print(sourceFile.getLocationMessage(message, begin, end, true, (x) => x));
     } else {
       print(message);
     }
   };
 }