Introduce a new IL instruction that does charCodeAt from
1- and 2-byte character strings. The existing CheckArrayBound
instructions is extended to be used for string bounds checking.
Also fix a bug with a missing compile-time bounds-check on constant
arrays.
TEST=tests/language/optimized_string_charcodeat.dart,
tests/language/optimized_constant_array_string_access.dart
Review URL: https://codereview.chromium.org//11360033
git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@14441 260f80e4-7a28-3924-810f-c04153c831b5
fschneider@google.com