Fix clang build by moving ToLowerASCII into base namespace.

base/string_util.h

Index: base/string_util.h
diff --git a/base/string_util.h b/base/string_util.h
index 186679e8f72c91460ae00329e99974a4d9cae9c8..c238e4afe82d13e3f1a4e626e04d9a7c1fa01ebc 100644
--- a/base/string_util.h
+++ b/base/string_util.h
@@ -116,6 +116,12 @@ size_t wcslcpy(wchar_t* dst, const wchar_t* src, size_t dst_size);
 // This function is intended to be called from base::vswprintf.
 bool IsWprintfFormatPortable(const wchar_t* format);
 
+// ASCII-specific tolower.  The standard library's tolower is locale sensitive,
+// so we don't want to use it here.
+template <class Char> inline Char ToLowerASCII(Char c) {
+  return (c >= 'A' && c <= 'Z') ? (c + ('a' - 'A')) : c;
+}
+
 // Function objects to aid in comparing/searching strings.
 
 template<typename Char> struct CaseInsensitiveCompare {
@@ -275,17 +281,11 @@ bool IsStringASCII(const std::wstring& str);
 bool IsStringASCII(const base::StringPiece& str);
 bool IsStringASCII(const string16& str);
 
-// ASCII-specific tolower.  The standard library's tolower is locale sensitive,
-// so we don't want to use it here.
-template <class Char> inline Char ToLowerASCII(Char c) {
-  return (c >= 'A' && c <= 'Z') ? (c + ('a' - 'A')) : c;
-}
-
 // Converts the elements of the given string.  This version uses a pointer to
 // clearly differentiate it from the non-pointer variant.
 template <class str> inline void StringToLowerASCII(str* s) {
   for (typename str::iterator i = s->begin(); i != s->end(); ++i)
-    *i = ToLowerASCII(*i);
+    *i = base::ToLowerASCII(*i);
 }
 
 template <class str> inline str StringToLowerASCII(const str& s) {