Remove root resource id aliasing from DriveResourceMetadata.

chrome/browser/chromeos/drive/drive_resource_metadata.h

Index: chrome/browser/chromeos/drive/drive_resource_metadata.h
diff --git a/chrome/browser/chromeos/drive/drive_resource_metadata.h b/chrome/browser/chromeos/drive/drive_resource_metadata.h
index 5ba131ac6ebdb23dc8468209e2f961397e210411..f43427e45dde3349d3d98442609bcfaa0aca3a11 100644
--- a/chrome/browser/chromeos/drive/drive_resource_metadata.h
+++ b/chrome/browser/chromeos/drive/drive_resource_metadata.h
@@ -133,7 +133,6 @@ class DriveResourceMetadata {
  public:
   // |root_resource_id| is the resource id for the root directory.
   DriveResourceMetadata(
-      const std::string& root_resource_id,
       const base::FilePath& data_directory_path,
       scoped_refptr<base::SequencedTaskRunner> blocking_task_runner);
 
@@ -383,8 +382,6 @@ class DriveResourceMetadata {
 
   scoped_ptr<DriveResourceMetadataStorage> storage_;
 
-  std::string root_resource_id_;
-
   base::Time last_serialized_;
   size_t serialized_size_;