Previously, the byte array get and set routines for integers would not
correctly narrow an integer when the width of a value being stored was
greater than the element width. This change implements the behavior in
the Web IDL specification.
In addition, an implementation for uint64 get and set is now provided.
BUG=2042
Review URL: https://chromiumcodereview.appspot.com//9769013
git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@5738 260f80e4-7a28-3924-810f-c04153c831b5