Pull in ASCII<->UTF16 from Chromium

base/strings/string_util.cc

+// Copyright 2013 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.
+
+#include "base/strings/string_util.h"
+
+namespace base {
+
+bool IsStringASCII(const StringPiece& str) {
+  for (size_t i = 0; i < str.length(); ++i)

[scottmg, 2015/05/04 23:15:33]

The Chromium implementation of these is surprisingly ... fancy.

+    if (str.data()[i] >= 0x80)
+      return false;
+  return true;
+}
+
+bool IsStringASCII(const StringPiece16& str) {
+  for (size_t i = 0; i < str.length(); ++i)
+    if (str.data()[i] >= 0x80)
+      return false;
+  return true;
+}
+
+}  // namespace base