Set root resource ID upon full feed update.

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 f30d8cdb5005c9add8fb0bdbde759aac7be84885..ddff53bd01e8da9f69c062029e7272fc98061ad2 100644
--- a/chrome/browser/chromeos/drive/drive_resource_metadata.h
+++ b/chrome/browser/chromeos/drive/drive_resource_metadata.h
@@ -58,9 +58,11 @@ std::string ContentOriginToString(ContentOrigin origin);
 // name is used in URLs for the file manager, hence user-visible.
 const FilePath::CharType kDriveRootDirectory[] = FILE_PATH_LITERAL("drive");
 
-// The resource ID for the root directory is defined in the spec:
+// The resource ID for the root directory for WAPI is defined in the spec:
 // https://developers.google.com/google-apps/documents-list/
-const char kDriveRootDirectoryResourceId[] = "folder:root";
+// Note that this special ID only applies to WAPI. Drive uses a non-constant
+// unique ID given in About resource.
+const char kWAPIRootDirectoryResourceId[] = "folder:root";
 
 // This should be incremented when incompatibility change is made in
 // drive.proto.
@@ -160,8 +162,8 @@ class DriveResourceMetadata {
   // Creates a DriveDirectory instance.
   scoped_ptr<DriveDirectory> CreateDriveDirectory();
 
-  // Sets root directory resource id and initialize the root entry.
-  void InitializeRootEntry(const std::string& root_id);
+  // Sets root directory resource ID and put root to ResourceMap.
+  void InitializeRootEntry(const std::string& id);
 
   // Add |doc entry| to directory with path |directory_path| and invoke the
   // callback asynchronously.