dart2js cps: Clone small constants to use site.

tests/compiler/dart2js/js_backend_cps_ir_basic_test.dart

 // Copyright (c) 2014, 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.
 
 // Tests for basic functionality.
 
 library basic_tests;
 
 import 'js_backend_cps_ir.dart';
 
@@ skipping 59 matching lines @@
   a = b;
   b = t;
   print(a);
   print(b);
   print(b);
   print(foo(a));
 }
   """,
   """
 function() {
-  var a = 10, b = 1;
-  P.print(b);
-  P.print(a);
-  P.print(a);
-  P.print(V.foo(b));
+  P.print(1);
+  P.print(10);
+  P.print(10);
+  P.print(V.foo(1));
 }"""),
   const TestEntry(
   """
 foo() { print(42); return 42; }
 main() { return foo(); }
   """,
   """function() {
   return V.foo();
 }"""),
   const TestEntry("main() {}"),
@@ skipping 47 matching lines @@
 """, r"""
 function() {
   V.foo();
 }"""),
   // Static setters
   const TestEntry("""
 var foo = 0;
 main() { print(foo = 42); }
 """, r"""
 function() {
-  var v0 = 42;
-  $.foo = v0;
-  P.print(v0);
+  $.foo = 42;
+  P.print(42);
 }"""),
   const TestEntry("""
 set foo(x) { print(x); }
 main() { foo = 42; }
 """, r"""
 function() {
   V.foo(42);
 }"""),
   // Assert
   const TestEntry("""
 foo() { print('X'); }
 main() {
   assert(true);
   assert(false);
   assert(foo());
   print('Done');
 }""", r"""
 function() {
   P.print("Done");
 }""")
 ];
 
 
 void main() {
   runTests(tests);
 }