In the past, characters in C strings were assumed to encode themselves
and when converting Dart strings to C strings characters were narrowed
to 8-bit values.
With this change, C strings are assumed to be UTF-8 encoded.
Converting a C string to a Dart string applies UTF-8 decoding and
converting a Dart string to a C string applies UTF-8 encoding.
Also part of this change are new methods to construct uninitialized
string objects and to copy string data.
BUG=5343358
Review URL: https://chromereviews.googleplex.com/3557012
git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@169 260f80e4-7a28-3924-810f-c04153c831b5
cshapiro@google.com