Optimize case conversion with icu_case_mapping

src/string-case.h

Index: src/string-case.h
diff --git a/src/string-case.h b/src/string-case.h
new file mode 100644
index 0000000000000000000000000000000000000000..3fe3bc2b819fed0076079338e9c15bd04a0fa313
--- /dev/null
+++ b/src/string-case.h
@@ -0,0 +1,17 @@
+// Copyright 2016 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef V8_STRING_CASE_H_
+#define V8_STRING_CASE_H_
+
+namespace v8 {
+namespace internal {
+
+template <bool is_lower>
+int FastAsciiConvert(char* dst, const char* src, int length, bool* changed_out);
+
+}  // namespace internal
+}  // namespace v8
+
+#endif  // V8_STRING_CASE_H__