Add explicit base namespace to string16 users.

chrome/common/net/url_util.cc

Index: chrome/common/net/url_util.cc
diff --git a/chrome/common/net/url_util.cc b/chrome/common/net/url_util.cc
index aaeb95e0b6496900d496d974085b1ec89b6f6ca5..3015a1737e68043b411b85f7dcd1fd64e4f6f3d3 100644
--- a/chrome/common/net/url_util.cc
+++ b/chrome/common/net/url_util.cc
@@ -21,7 +21,7 @@ void WriteURLToClipboard(const GURL& url,
 
   // Unescaping path and query is not a good idea because other applications
   // may not encode non-ASCII characters in UTF-8.  See crbug.com/2820.
-  string16 text = url.SchemeIs(content::kMailToScheme) ?
+  base::string16 text = url.SchemeIs(content::kMailToScheme) ?
       ASCIIToUTF16(url.path()) :
       net::FormatUrl(url, languages, net::kFormatUrlOmitNothing,
                      net::UnescapeRule::NONE, NULL, NULL, NULL);