[regexp] implement character classes for unicode regexps.

src/regexp/regexp-ast.cc

Index: src/regexp/regexp-ast.cc
diff --git a/src/regexp/regexp-ast.cc b/src/regexp/regexp-ast.cc
index 31c93b114f14d0f0bb03be1b0f7ba499a616b0d0..b5c2bb6d91d9f3b060366171a21bf645ff8a805a 100644
--- a/src/regexp/regexp-ast.cc
+++ b/src/regexp/regexp-ast.cc
@@ -172,9 +172,9 @@ void* RegExpUnparser::VisitAlternative(RegExpAlternative* that, void* data) {
 
 
 void RegExpUnparser::VisitCharacterRange(CharacterRange that) {
-  os_ << AsUC16(that.from());
+  os_ << AsUC32(that.from());
   if (!that.IsSingleton()) {
-    os_ << "-" << AsUC16(that.to());
+    os_ << "-" << AsUC32(that.to());
   }
 }