Fix Unicode issues in dart2js and dart2dart.

tests/co19/co19-dart2js.status

Index: tests/co19/co19-dart2js.status
diff --git a/tests/co19/co19-dart2js.status b/tests/co19/co19-dart2js.status
index 3c83972eefba1b81e69c5205f22c41f0034cb91e..72876c8c757fe6c5453e3cebd976e8cb6f5d09c2 100644
--- a/tests/co19/co19-dart2js.status
+++ b/tests/co19/co19-dart2js.status
@@ -377,9 +377,8 @@ Language/11_Expressions/32_Type_Cast_A01_t04: Fail, OK # co19 issue 241
 
 Language/11_Expressions/22_Equality_A01_t01: Fail, OK # Function declaration takes precedence over function expression.
 Language/11_Expressions/28_Postfix_Expressions_A01_t01: Fail, OK # A map literal cannot start an expression statement.
-LibTest/core/String/String_class_A02_t01: Pass, Fail, OK # issue 6418 compiler cancelled: Unhandled non-BMP character: U+10000
-LibTest/core/String/charCodeAt_A01_t01: Fail, OK # compiler cancelled: Unhandled non-BMP character: U+10000
-LibTest/core/String/charCodes_A01_t01: Fail, OK # compiler cancelled: Unhandled non-BMP character: U+10000
+LibTest/core/String/String_class_A02_t01: Fail, OK # co19 issue 284
+LibTest/core/String/charCodeAt_A01_t01: Fail, OK # charCodeAt can't be used to get supplementary characters.
 
 Language/06_Functions/1_Function_Declaration_A02_t03: Fail, OK # co19 issue 210
 Language/06_Functions/1_Function_Declaration_A03_t03: Fail, OK # co19 issue 210