Revert "Revert "ASCII <-> UTF16 conversion functions. These are just copies of WideToASCII and""

base/string_util.cc

Index: base/string_util.cc
diff --git a/base/string_util.cc b/base/string_util.cc
index 4ba8c4b98d5aeb059d2d9fd0030d9b1e4a8fec82..d84fadb75e6558a1e5b3cb0a870c059890b9b242 100644
--- a/base/string_util.cc
+++ b/base/string_util.cc
@@ -450,6 +450,16 @@ std::wstring ASCIIToWide(const std::string& ascii) {
   return std::wstring(ascii.begin(), ascii.end());
 }
 
+std::string UTF16ToASCII(const string16& utf16) {
+  DCHECK(IsStringASCII(utf16));
+  return std::string(utf16.begin(), utf16.end());
+}
+
+string16 ASCIIToUTF16(const std::string& ascii) {
+  DCHECK(IsStringASCII(ascii));
+  return string16(ascii.begin(), ascii.end());
+}
+
 // Latin1 is just the low range of Unicode, so we can copy directly to convert.
 bool WideToLatin1(const std::wstring& wide, std::string* latin1) {
   std::string output;
@@ -472,20 +482,28 @@ bool IsString8Bit(const std::wstring& str) {
   return true;
 }
 
-bool IsStringASCII(const std::wstring& str) {
+template<class STR>
+static bool DoIsStringASCII(const STR& str) {
   for (size_t i = 0; i < str.length(); i++) {
-    if (str[i] > 0x7F)
+    typename ToUnsigned<typename STR::value_type>::Unsigned c = str[i];
+    if (c > 0x7F)
       return false;
   }
   return true;
 }
 
+bool IsStringASCII(const std::wstring& str) {
+  return DoIsStringASCII(str);
+}
+
+#if !defined(WCHAR_T_IS_UTF16)
+bool IsStringASCII(const string16& str) {
+  return DoIsStringASCII(str);
+}
+#endif
+
 bool IsStringASCII(const std::string& str) {
-  for (size_t i = 0; i < str.length(); i++) {
-    if (static_cast<unsigned char>(str[i]) > 0x7F)
-      return false;
-  }
-  return true;
+  return DoIsStringASCII(str);
 }
 
 // Helper functions that determine whether the given character begins a