Update from https://crrev.com/328418

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 9ead9c14bf2c2758f101036219525c27a5d409e8..99f1a7c6814753ec9b1d63a85930399eddb0eeab 100644
--- a/base/files/important_file_writer.h
+++ b/base/files/important_file_writer.h
@@ -78,7 +78,7 @@ class BASE_EXPORT ImportantFileWriter : public NonThreadSafe {
 
   // Save |data| to target filename. Does not block. If there is a pending write
   // scheduled by ScheduleWrite, it is cancelled.
-  void WriteNow(const std::string& data);
+  void WriteNow(scoped_ptr<std::string> data);
 
   // Schedule a save to target filename. Data will be serialized and saved
   // to disk after the commit interval. If another ScheduleWrite is issued
@@ -106,7 +106,7 @@ class BASE_EXPORT ImportantFileWriter : public NonThreadSafe {
 
  private:
   // Helper method for WriteNow().
-  bool PostWriteTask(const std::string& data);
+  bool PostWriteTask(const Callback<bool()>& task);
 
   // If |result| is true and |on_next_successful_write_| is set, invokes
   // |on_successful_write_| and then resets it; no-ops otherwise.