Explicitly check various sync_file_system classes live on the IO thread.

chrome/browser/sync_file_system/local/syncable_file_operation_runner.h

Index: chrome/browser/sync_file_system/local/syncable_file_operation_runner.h
diff --git a/chrome/browser/sync_file_system/local/syncable_file_operation_runner.h b/chrome/browser/sync_file_system/local/syncable_file_operation_runner.h
index 9db926413ad5876810f517f7a7a624a714cd4e28..cadbf89c573cb7d03acb0dd40448dad35633b762 100644
--- a/chrome/browser/sync_file_system/local/syncable_file_operation_runner.h
+++ b/chrome/browser/sync_file_system/local/syncable_file_operation_runner.h
@@ -14,7 +14,6 @@
 #include "base/callback.h"
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
-#include "base/threading/non_thread_safe.h"
 #include "chrome/browser/sync_file_system/local/local_file_sync_status.h"
 #include "storage/browser/fileapi/file_system_url.h"
 
@@ -27,8 +26,7 @@ namespace sync_file_system {
 // This class must run only on IO thread.
 // Owned by LocalFileSyncContext.
 class SyncableFileOperationRunner
-    : public base::NonThreadSafe,
-      public base::SupportsWeakPtr<SyncableFileOperationRunner>,
+    : public base::SupportsWeakPtr<SyncableFileOperationRunner>,
       public LocalFileSyncStatus::Observer {
  public:
   // Represents an operation task (which usually wraps one FileSystemOperation).
@@ -49,7 +47,6 @@ class SyncableFileOperationRunner
     friend class SyncableFileOperationRunner;
     bool IsRunnable(LocalFileSyncStatus* status) const;
     void Start(LocalFileSyncStatus* status);
-    static void CancelAndDelete(Task* task);
 
     DISALLOW_COPY_AND_ASSIGN(Task);
   };
@@ -91,9 +88,9 @@ class SyncableFileOperationRunner
   bool ShouldStartMoreTasks() const;
 
   // Keeps track of the writing/syncing status. Not owned.
-  LocalFileSyncStatus* sync_status_;
+  LocalFileSyncStatus* const sync_status_;
 
-  std::list<Task*> pending_tasks_;
+  std::list<std::unique_ptr<Task>> pending_tasks_;
 
   const int64_t max_inflight_tasks_;
   int64_t num_inflight_tasks_;