fix #470, string interpolation now respects Dart toString

test/codegen/expect/DeltaBlue.js

Index: test/codegen/expect/DeltaBlue.js
diff --git a/test/codegen/expect/DeltaBlue.js b/test/codegen/expect/DeltaBlue.js
index 49eaa16fef56d324f9ee6733bbb39d640df92a35..1dee3e0972500c05974509eb5bc6b6dcc672965a 100644
--- a/test/codegen/expect/DeltaBlue.js
+++ b/test/codegen/expect/DeltaBlue.js
@@ -52,7 +52,7 @@ dart_library.library('DeltaBlue', null, /* Imports */[
     }
     report() {
       let score = this.measure();
-      core.print(`${this.name}(RunTime): ${score} us.`);
+      core.print(dart.str`${this.name}(RunTime): ${score} us.`);
     }
   };
   dart.setSignature(BenchmarkBase$.BenchmarkBase, {
@@ -532,7 +532,7 @@ dart_library.library('DeltaBlue', null, /* Imports */[
       plan.execute();
       if (last.value != i) {
         core.print("Chain test failed:");
-        core.print(`Expected last value to be ${i} but it was ${last.value}.`);
+        core.print(dart.str`Expected last value to be ${i} but it was ${last.value}.`);
       }
     }
   };
@@ -578,12 +578,12 @@ dart_library.library('DeltaBlue', null, /* Imports */[
   BenchmarkBase$.Expect = class Expect extends core.Object {
     static equals(expected, actual) {
       if (!dart.equals(expected, actual)) {
-        dart.throw(`Values not equal: ${expected} vs ${actual}`);
+        dart.throw(dart.str`Values not equal: ${expected} vs ${actual}`);
       }
     }
     static listEquals(expected, actual) {
       if (expected[dartx.length] != actual[dartx.length]) {
-        dart.throw(`Lists have different lengths: ${expected[dartx.length]} vs ${actual[dartx.length]}`);
+        dart.throw(dart.str`Lists have different lengths: ${expected[dartx.length]} vs ${actual[dartx.length]}`);
       }
       for (let i = 0; i < dart.notNull(actual[dartx.length]); i++) {
         BenchmarkBase$.Expect.equals(expected[dartx.get](i), actual[dartx.get](i));