Extend and refactor GDataFileBase and derived classes.

chrome/browser/chromeos/gdata/gdata_file_system_unittest.cc

Index: chrome/browser/chromeos/gdata/gdata_file_system_unittest.cc
===================================================================
--- chrome/browser/chromeos/gdata/gdata_file_system_unittest.cc	(revision 126207)
+++ chrome/browser/chromeos/gdata/gdata_file_system_unittest.cc	(working copy)
@@ -553,14 +553,14 @@
   GDataFileBase* file = NULL;
   EXPECT_TRUE((file = FindFile(file_in_root)) != NULL);
   EXPECT_TRUE(file->AsGDataFile() != NULL);
-  std::string file_in_root_resource = file->AsGDataFile()->resource();
+  std::string file_in_root_resource = file->AsGDataFile()->resource_id();
   EXPECT_EQ(file, FindFileByResource(file_in_root_resource));
 
   EXPECT_TRUE(FindFile(dir_in_root) != NULL);
 
   EXPECT_TRUE((file = FindFile(file_in_subdir)) != NULL);
   EXPECT_TRUE(file->AsGDataFile() != NULL);
-  std::string file_in_subdir_resource = file->AsGDataFile()->resource();
+  std::string file_in_subdir_resource = file->AsGDataFile()->resource_id();
   EXPECT_EQ(file, FindFileByResource(file_in_subdir_resource));
 
   // Remove first file in root.