Reduce usage of MessageLoopProxy in base/

base/files/important_file_writer.h

Index: base/files/important_file_writer.h
diff --git a/base/files/important_file_writer.h b/base/files/important_file_writer.h
index 61a53b16503bda6902519df11c60278096979f11..9ead9c14bf2c2758f101036219525c27a5d409e8 100644
--- a/base/files/important_file_writer.h
+++ b/base/files/important_file_writer.h
@@ -62,8 +62,9 @@ class BASE_EXPORT ImportantFileWriter : public NonThreadSafe {
   // |task_runner| is the SequencedTaskRunner instance where on which we will
   // execute file I/O operations.
   // All non-const methods, ctor and dtor must be called on the same thread.
-  ImportantFileWriter(const FilePath& path,
-                      base::SequencedTaskRunner* task_runner);
+  ImportantFileWriter(
+      const FilePath& path,
+      const scoped_refptr<base::SequencedTaskRunner>& task_runner);
 
   // You have to ensure that there are no pending writes at the moment
   // of destruction.