Move IsStringASCII/UTF8 to base namespace.

net/base/net_util.cc

Index: net/base/net_util.cc
diff --git a/net/base/net_util.cc b/net/base/net_util.cc
index 0174c653f83065c3ef48fd90a31254d0d4d4b03c..7e3e514e00a73228695bf0a605227d5a47b16db9 100644
--- a/net/base/net_util.cc
+++ b/net/base/net_util.cc
@@ -802,7 +802,7 @@ std::string GetFileNameFromURL(const GURL& url,
 
   // The URL's path should be escaped UTF-8, but may not be.
   std::string decoded_filename = unescaped_url_filename;
-  if (!IsStringUTF8(decoded_filename)) {
+  if (!base::IsStringUTF8(decoded_filename)) {
     // TODO(jshin): this is probably not robust enough. To be sure, we need
     // encoding detection.
     base::string16 utf16_output;