restructure string decoding to support iterable use and include benchmarks for UTF-8 decoding.

utils/tests/string_encoding/unicode_core_tests.dart

 #!/usr/bin/env 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.
 
 #library("unicode_core_tests");
 #import("dunit.dart");
 #import("../../string_encoding/unicode_core.dart");
 
 void main() {
   TestSuite suite = new TestSuite();
   suite.registerTestClass(new UnicodeCoreTests());
   suite.run();
 }
 
 class UnicodeCoreTests extends TestClass {
   void registerTests(TestSuite suite) {
     register("testPlatform", testPlatform, suite);
     register("testCodepointsToUtf16CodeUnits",
         testCodepointsToUtf16CodeUnits, suite);
     register("testUtf16bytesToCodepoints", testUtf16bytesToCodepoints, suite);
   }
 
   void testPlatform() {
     Expect.isFalse(is16BitCodeUnit());
   }
 
   void testCodepointsToUtf16CodeUnits() {
     // boundary conditions
+    Expect.listEquals([], codepointsToUtf16CodeUnits([]), "no input");
     Expect.listEquals([0x0], codepointsToUtf16CodeUnits([0x0]), "0");
     Expect.listEquals([0xd800, 0xdc00],
         codepointsToUtf16CodeUnits([0x10000]), "10000");
 
     Expect.listEquals([0xffff],
         codepointsToUtf16CodeUnits([0xffff]), "ffff");
     Expect.listEquals([0xdbff, 0xdfff],
         codepointsToUtf16CodeUnits([0x10ffff]), "10ffff");
 
     Expect.listEquals([0xd7ff],
         codepointsToUtf16CodeUnits([0xd7ff]), "d7ff");
     Expect.listEquals([0xe000],
         codepointsToUtf16CodeUnits([0xe000]), "e000");
 
     Expect.listEquals([UNICODE_REPLACEMENT_CHARACTER_CODEPOINT],
         codepointsToUtf16CodeUnits([0xd800]), "d800");
     Expect.listEquals([UNICODE_REPLACEMENT_CHARACTER_CODEPOINT],
         codepointsToUtf16CodeUnits([0xdfff]), "dfff");
   }
 
   void testUtf16bytesToCodepoints() {
     // boundary conditions: First possible values
+    Expect.listEquals([], utf16CodeUnitsToCodepoints([]), "no input");
     Expect.listEquals([0x0], utf16CodeUnitsToCodepoints([0x0]), "0");
     Expect.listEquals([0x10000],
         utf16CodeUnitsToCodepoints([0xd800, 0xdc00]), "10000");
 
     // boundary conditions: Last possible sequence of a certain length
     Expect.listEquals([0xffff],
         utf16CodeUnitsToCodepoints([0xffff]), "ffff");
     Expect.listEquals([0x10ffff],
         utf16CodeUnitsToCodepoints([0xdbff, 0xdfff]), "10ffff");
 
@@ skipping 32 matching lines @@
         "d800 dbff last byte missing");
 
     // impossible bytes
     Expect.listEquals([0xfffd], utf16CodeUnitsToCodepoints([0x110000]),
         "110000 out of bounds");
 
     // overlong sequences not possible in utf16 (nothing < x10000)
     // illegal code positions d800-dfff not encodable (< x10000)
   }
 }