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

url/gurl.h

Index: url/gurl.h
diff --git a/url/gurl.h b/url/gurl.h
index e830b1a3ec7c74f46fbe5d370944720aca89c380..cf5785a56c6cf4aa1f8551ef1edfe32bcad3b506 100644
--- a/url/gurl.h
+++ b/url/gurl.h
@@ -222,12 +222,12 @@ class URL_EXPORT GURL {
   // We often need to know if this is a file URL. File URLs are "standard", but
   // are often treated separately by some programs.
   bool SchemeIsFile() const {
-    return SchemeIs("file");
+    return SchemeIs(url::kFileScheme);
   }
 
   // FileSystem URLs need to be treated differently in some cases.
   bool SchemeIsFileSystem() const {
-    return SchemeIs("filesystem");
+    return SchemeIs(url::kFileSystemScheme);
   }
 
   // If the scheme indicates a secure connection