Optimize _GrowableArray._join and _StringBase._interpolate.

tests/corelib/iterable_join_test.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.
 
 import "package:expect/expect.dart";
 
 class IC {
   int count = 0;
   String toString() => "${count++}";
 }
@@ skipping 52 matching lines @@
   testArray(const [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]);
 
   testJoin("a,b,c,d", ["a", "b", "c", "d"].map((x) => x), ",");
   testJoin("abcd", ["a", "b", "c", "d"].map((x) => x), "");
   testJoin("abcd", ["a", "b", "c", "d"].map((x) => x));
   testJoin("null,b,c,d", [null,"b","c","d"].map((x) => x), ",");
   testJoin("1,2,3,4", [1, 2, 3, 4].map((x) => x), ",");
   testJoin("4,5,6,7", [ic, ic, ic, ic].map((x) => x), ",");
 }
 
+void testStringVariants() {
+  // ASCII
+  testJoin("axbxcxd", ["a", "b", "c", "d"], "x");
+  testJoin("a\u2000b\u2000c\u2000d", ["a", "b", "c", "d"], "\u2000");
+  testJoin("abcd", ["a", "b", "c", "d"], "");
+  testJoin("abcd", ["a", "b", "c", "d"]);
+  // Non-ASCII
+  testJoin("axbxcx\u2000", ["a", "b", "c", "\u2000"], "x");
+  testJoin("a\u2000b\u2000c\u2000\u2000", ["a", "b", "c", "\u2000"], "\u2000");
+  testJoin("abc\u2000", ["a", "b", "c", "\u2000"], "");
+  testJoin("abc\u2000", ["a", "b", "c", "\u2000"]);
+  // Long-ASCII
+  testJoin("ax" * 255 + "a", new List.generate(256, (_) => "a"), "x");
+  testJoin("a" * 256, new List.generate(256, (_) => "a"));
+  // Long-Non-ASCII
+  testJoin("a\u2000" * 255 + "a", new List.generate(256, (_) => "a"), "\u2000");
+  testJoin("\u2000" * 256, new List.generate(256, (_) => "\u2000"));
+  testJoin("\u2000x" * 255 + "\u2000",
+           new List.generate(256, (_) => "\u2000"), "x");
+
+  var o1 = new Stringable("x");
+  var o2 = new Stringable("\ufeff");
+  testJoin("xa" * 3 + "x", [o1, o1, o1, o1], "a");
+  testJoin("x" * 4, [o1, o1, o1, o1], "");
+  testJoin("x" * 4, [o1, o1, o1, o1]);
+
+  testJoin("\ufeffx" * 3 + "\ufeff", [o2, o2, o2, o2], "x");
+  testJoin("\ufeff" * 4, [o2, o2, o2, o2], "");
+  testJoin("\ufeff" * 4, [o2, o2, o2, o2]);
+
+  testJoin("a\u2000x\ufeff", ["a", "\u2000", o1, o2]);
+  testJoin("a\u2000\ufeffx", ["a", "\u2000", o2, o1]);
+  testJoin("ax\u2000\ufeff", ["a", o1, "\u2000", o2]);
+  testJoin("ax\ufeff\u2000", ["a", o1, o2, "\u2000"]);
+  testJoin("a\ufeffx\u2000", ["a", o2, o1, "\u2000"]);
+  testJoin("a\ufeff\u2000x", ["a", o2, "\u2000", o1]);
+
+  testJoin("\u2000ax\ufeff", ["\u2000", "a", o1, o2]);
+  testJoin("\u2000a\ufeffx", ["\u2000", "a", o2, o1]);
+  testJoin("xa\u2000\ufeff", [o1, "a", "\u2000", o2]);
+  testJoin("xa\ufeff\u2000", [o1, "a", o2, "\u2000"]);
+  testJoin("\ufeffax\u2000", [o2, "a", o1, "\u2000"]);
+  testJoin("\ufeffa\u2000x", [o2, "a", "\u2000", o1]);
+
+  testJoin("\u2000xa\ufeff", ["\u2000", o1, "a", o2]);
+  testJoin("\u2000\ufeffax", ["\u2000", o2, "a", o1]);
+  testJoin("x\u2000a\ufeff", [o1, "\u2000", "a", o2]);
+  testJoin("x\ufeffa\u2000", [o1, o2, "a", "\u2000"]);
+  testJoin("\ufeffxa\u2000", [o2, o1, "a", "\u2000"]);
+  testJoin("\ufeff\u2000ax", [o2, "\u2000", "a", o1]);
+
+  testJoin("\u2000x\ufeffa", ["\u2000", o1, o2, "a"]);
+  testJoin("\u2000\ufeffxa", ["\u2000", o2, o1, "a"]);
+  testJoin("x\u2000\ufeffa", [o1, "\u2000", o2, "a"]);
+  testJoin("x\ufeff\u2000a", [o1, o2, "\u2000", "a"]);
+  testJoin("\ufeffx\u2000a", [o2, o1, "\u2000", "a"]);
+  testJoin("\ufeff\u2000xa", [o2, "\u2000", o1, "a"]);
+}
+
+class Stringable {
+  final String value;
+  Stringable(this.value);
+  String toString() => value;
+}
+
 main() {
   testCollections();
+  testStringVariants();
   // TODO(lrn): test scalar lists.
 }