Replace some hard coded schemes with the constants in /url/url_constants.h.

url/url_constants.cc

Index: url/url_constants.cc
diff --git a/url/url_constants.cc b/url/url_constants.cc
index d5c57f487aff4de46f66abdad823b67376731787..9ef0e632693da6c222033dc5119c51b14e4010eb 100644
--- a/url/url_constants.cc
+++ b/url/url_constants.cc
@@ -14,6 +14,7 @@ const char kDataScheme[] = "data";
 const char kFileScheme[] = "file";
 const char kFileSystemScheme[] = "filesystem";
 const char kFtpScheme[] = "ftp";
+const char kGopherScheme[] = "gopher";
 const char kHttpScheme[] = "http";
 const char kHttpsScheme[] = "https";
 const char kJavaScriptScheme[] = "javascript";