dart2js cps: Do not inline string interpolation helper.

tests/compiler/dart2js/cps_ir/expected/gvn_1.js

 // Expectation for test: 
 // foo(x, list) {
 //   var sum = 0;
 //   for (int k = 0; k < 10; k++) {
 //     // Everything can be hoisted out up to the index access which is
 //     // blocked by the bounds check.
 //     var a = x.left.left;
 //     var b = x.left.right;
 //     var c = x.right.left;
 //     var d = x.right.right;
@@ skipping 27 matching lines @@
 //   var y2 = new Branch(x3, x4);
 //   var z  = new Root(y1, y2);
 //   print(foo(z, [1,2,3,4,5,6,7,8,9,10]));
 // }
 
 function() {
   var v0 = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10], i = 1 + 20, v1 = i * (10 + -10), sum = 0, k = 0, line;
   for (; k < 10; sum += i + v0[v1], ++k)
     if (v1 < 0 || v1 >= 10)
       return H.ioore(v0, v1);
-  line = sum === 0 ? 1 / sum < 0 ? "-0.0" : "" + sum : "" + sum;
+  line = H.S(sum);
   if (typeof dartPrint == "function")
     dartPrint(line);
   else if (typeof console == "object" && typeof console.log != "undefined")
     console.log(line);
   else if (!(typeof window == "object")) {
     if (!(typeof print == "function"))
       throw "Unable to print message: " + String(line);
     print(line);
   }
 }