Optimize case conversion with icu_case_mapping

BUILD.gn

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/config/android/config.gni")
 import("//build/config/arm.gni")
 import("//build/config/dcheck_always_on.gni")
 import("//build/config/mips.gni")
 import("//build/config/sanitizers/sanitizers.gni")
 
@@ skipping 1664 matching lines @@
     "src/source-position-table.cc",
     "src/source-position-table.h",
     "src/source-position.cc",
     "src/source-position.h",
     "src/splay-tree-inl.h",
     "src/splay-tree.h",
     "src/startup-data-util.cc",
     "src/startup-data-util.h",
     "src/string-builder.cc",
     "src/string-builder.h",
+    "src/string-case.cc",
+    "src/string-case.h",
     "src/string-search.h",
     "src/string-stream.cc",
     "src/string-stream.h",
     "src/strtod.cc",
     "src/strtod.h",
     "src/tracing/trace-event.cc",
     "src/tracing/trace-event.h",
     "src/tracing/traced-value.cc",
     "src/tracing/traced-value.h",
     "src/tracing/tracing-category-observer.cc",
@@ skipping 1291 matching lines @@
   ]
 
   configs = [
     ":external_config",
     ":internal_config_base",
   ]
 }
 
 v8_fuzzer("wasm_data_section_fuzzer") {
 }