Move UTF16ToASCII, remove WideToASCII.

This removes WideToASCII and changes all callers to use UTF16ToASCII instead.

Moves UTF16ToASCII from base/strings/string_util.h to base/strings/utf_string_conversions.h and into the base namespace.

Convert a few related string_util functions to take a StringPiece16 instead of a string16. Remove IsStringASCII(std::wstring) which was unused.

Updates callers' includes and namespace usage accordingly.

TBR=sky

Review URL: https://codereview.chromium.org/176843022

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@257200 0039d316-1c4b-4281-b951-d872f2087c98


CrOS-Libchrome-Original-Commit: 74f778ee567a5e18ae6766416711b92fc6e7f39a
diff --git a/base/files/file_path.cc b/base/files/file_path.cc
index 3ea5856..d47becb 100644
--- a/base/files/file_path.cc
+++ b/base/files/file_path.cc
@@ -633,8 +633,8 @@
 
 std::string FilePath::MaybeAsASCII() const {
   if (IsStringASCII(path_))
-    return WideToASCII(path_);
-  return "";
+    return UTF16ToASCII(path_);
+  return std::string();
 }
 
 std::string FilePath::AsUTF8Unsafe() const {