Integrate registry_hash_store_contents with the rest of tracked prefs.

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 0bd8a7fd358f037ba26a8768a46b55627a112be3..7643d09b9b26245ecb79d3e1f1d36b14c5d797ff 100644
--- a/base/files/important_file_writer.h
+++ b/base/files/important_file_writer.h
@@ -100,6 +100,11 @@ class BASE_EXPORT ImportantFileWriter : public NonThreadSafe {
   void RegisterOnNextSuccessfulWriteCallback(

[gab, 2016/08/03 18:19:34]

Similar to comment below, suggest updating this to:

  // Registers |on_next_successful_write_reply| to be invoked on the sequence
  // owning this ImportantFileWriter in reply to the next successful write.
  void RegisterOnNextSuccessfulWriteReply(
    const Closure& on_next_successful_write_reply);

[proberge, 2016/08/04 00:13:45]

Done.

       const Closure& on_next_successful_write);
 
+  // Registers |on_next_successful_write| to be called once, on the next
+  // successful write event. Multiple callbacks can be set at once.

[gab, 2016/08/03 18:19:34]

Your implementation only allows a single callback, not multiple.

[proberge, 2016/08/04 00:13:45]

Done.

+  void RegisterOnNextSuccessfulWriteBlockingCallback(

[gab, 2016/08/03 18:19:34]

The ImportantFileWriter doesn't have a notion of the "BlockingPool", it just so
happens that |task_runner_| is bound to it in the JsonPrefStore's use case (and
even the JsonPrefStore doesn't know that either, it comes as a generic
SequencedTaskRunner from the factory in chrome).

Suggest:

  // Registers |on_next_successful_write_callback| to be synchronously invoked
  // from WriteFileAtomically() on its next successful write (i.e. from
  // |task_runner_|).
  void RegisterOnNextSuccessfulWriteSynchronousCallback(
      const Closure& on_next_successful_write_callback);

[proberge, 2016/08/04 00:13:45]

Done.

+      const Closure& on_next_successful_write);
+
   TimeDelta commit_interval() const {
     return commit_interval_;
   }
@@ -115,6 +120,10 @@ class BASE_EXPORT ImportantFileWriter : public NonThreadSafe {
   // Invoked once and then reset on the next successful write event.
   Closure on_next_successful_write_;

[gab, 2016/08/03 18:19:34]

on_next_successful_write_reply_

[proberge, 2016/08/04 00:13:45]

Done.

 
+  // Invoked on the blocking pool and then reset on the next successful write
+  // event.
+  Closure blocking_on_next_successful_write_;

[gab, 2016/08/03 18:19:34]

// Invoked synchronously on the next successful write and reset on this
ImportantFileWriter's owning sequence in the reply to such a write.
Closure on_next_successful_write_callback_;

[proberge, 2016/08/04 00:13:45]

Done.

+
   // Path being written to.
   const FilePath path_;