Fix bad canonicalization for strings whose utf32->utf16 conversion is lossy.

runtime/vm/object_test.cc

 // 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.
 
 #include "platform/globals.h"
 
 #include "vm/assembler.h"
 #include "vm/class_finalizer.h"
 #include "vm/dart_api_impl.h"
 #include "vm/dart_entry.h"
@@ skipping 4708 matching lines @@
   };
   String& test = String::Handle();
   String& result = String::Handle();
   for (size_t i = 0; i < ARRAY_SIZE(tests); i++) {
     test = String::New(tests[i].in);
     result = String::ScrubName(test);
     EXPECT_STREQ(tests[i].out, result.ToCString());
   }
 }
 
+
+VM_TEST_CASE(String_EqualsUTF32) {

[hausner, 2016/10/06 22:14:41]

Maybe a short comment what is being tested here and a reference to the bug
number?

[rmacnak, 2016/10/06 23:16:29]

Done.

+  int32_t char_codes[] = {
+    0, 0x0a, 0x0d, 0x7f, 0xff, 0xffff, 0xd800, 0xdc00, 0xdbff, 0xdfff
+  };
+
+  const String& str =
+      String::Handle(String::FromUTF32(char_codes, ARRAY_SIZE(char_codes)));
+  EXPECT(str.Equals(char_codes, ARRAY_SIZE(char_codes)));
+}
+
 }  // namespace dart