[regexp] Fix off-by-one in CharacterRange::Negate.

src/regexp/regexp-ast.h

Index: src/regexp/regexp-ast.h
diff --git a/src/regexp/regexp-ast.h b/src/regexp/regexp-ast.h
index 4a81ccaf1b4444042e653a3f1a3e7f4fa071638f..89cbf9b9ff94c0eacdb3bbddce680c7d57aa3765 100644
--- a/src/regexp/regexp-ast.h
+++ b/src/regexp/regexp-ast.h
@@ -78,7 +78,9 @@ class CharacterRange {
   CharacterRange() : from_(0), to_(0) {}
   // For compatibility with the CHECK_OK macro
   CharacterRange(void* null) { DCHECK_NULL(null); }  // NOLINT
-  CharacterRange(uc32 from, uc32 to) : from_(from), to_(to) {}
+  CharacterRange(uc32 from, uc32 to) : from_(from), to_(to) {
+    DCHECK(from <= to);
+  }
   static void AddClassEscape(uc16 type, ZoneList<CharacterRange>* ranges,
                              Zone* zone);
   static Vector<const int> GetWordBounds();