- Remove more String operator + from tests.

tests/language/src/OptimizationTest.dart

 // Copyright (c) 2011, 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 various optimizations and deoptimizations of optimizing compiler..
 
 addThem(a, b) {
   return a + b;
 }
 
 isItInt(a) {
@@ skipping 17 matching lines @@
 }
 
 doStore1(a, v) {
   a[1] = v;
 }
 
 doStore2(a, v) {
   a[2] = v;
 }
 
+class StringPlus {
+  const StringPlus(String this._val);
+  operator + (right) => new StringPlus("${_val}${right}");
+  toString() => _val;
+
+  final String _val;
+}
+
 main() {
   for (int i = 0; i < 2000; i++) {
-    Expect.stringEquals("HI 5", addThem("HI ", 5));
+    Expect.stringEquals("HI 5", addThem(const StringPlus("HI "), 5).toString());
     Expect.equals(true, isItInt(5));
   }
   Expect.equals(8, addThem(3, 5));
   for (int i = 0; i < 2000; i++) {
-    Expect.stringEquals("HI 5", addThem("HI ", 5));
+    Expect.stringEquals("HI 5", addThem(const StringPlus("HI "), 5).toString());
     Expect.equals(8, addThem(3, 5));
   }
   for (int i = -500; i < 500; i++) {
     var r = doNeg(i);
     var p = doNeg(r);
     Expect.equals(i, p);
   }
   var maxSmi = (1 << 30) - 1;
   Expect.equals(maxSmi, doNeg(doNeg(maxSmi)));
   // Deoptimize because of overflow.
@@ skipping 23 matching lines @@
     Expect.equals(7, fixed[1]);
     doStore2(growable, 12);
     Expect.equals(12, growable[2]);
   }
 
   // Deoptimize.
   doStore1(growable, 8);
   Expect.equals(8, growable[1]);
   doStore2(fixed, 101);
   Expect.equals(101, fixed[2]);
-}
+}