Cleanup: Remove some unused code, or make them platform specific.

chrome/browser/browsing_data/browsing_data_file_system_helper.h

Index: chrome/browser/browsing_data/browsing_data_file_system_helper.h
===================================================================
--- chrome/browser/browsing_data/browsing_data_file_system_helper.h	(revision 246675)
+++ chrome/browser/browsing_data/browsing_data_file_system_helper.h	(working copy)
@@ -144,23 +144,13 @@
   CannedBrowsingDataFileSystemHelper();
   virtual ~CannedBrowsingDataFileSystemHelper();
 
-  // Holds the current list of filesystems returned to the client. Access to
-  // |file_system_info_| is triggered indirectly via the UI thread and guarded
-  // by |is_fetching_|. This means |file_system_info_| is only accessed while
-  // |is_fetching_| is true. The flag |is_fetching_| is only accessed on the UI
-  // thread.
+  // Holds the current list of filesystems returned to the client.
   std::list<FileSystemInfo> file_system_info_;
 
   // The callback passed in at the beginning of the StartFetching workflow so
   // that it can be triggered via NotifyOnUIThread.
   base::Callback<void(const std::list<FileSystemInfo>&)> completion_callback_;
 
-  // Indicates whether or not we're currently fetching information: set to true
-  // when StartFetching is called on the UI thread, and reset to false when
-  // NotifyOnUIThread triggers the success callback.
-  // This property only mutates on the UI thread.
-  bool is_fetching_;
-
   DISALLOW_COPY_AND_ASSIGN(CannedBrowsingDataFileSystemHelper);
 };