accelerometer: Fix TryScheduleInitialize bug

Fixes <2079112a>: accelerometer: Refactor AccelerometerFileReader

TryScheduleInitialize should be run in |ui_task_runner_| instead of
|blocking_task_runner_|.

BUG=chromium:1164449
TEST=unit tests

Change-Id: If242c2ba3e20f88db5f94261621d671629a786ea
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2617414Reviewed-by: Ahmed Fakhry <afakhry@chromium.org>
Commit-Queue: Cheng-Hao Yang <chenghaoyang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#841789}

ash/accelerometer/accelerometer_file_reader.cc

@@ -373,7 +373,7 @@ void AccelerometerFileReader::SetStatesWithInitializationResult(
       // If we haven't yet passed the timeout cutoff, try this again. This will
       // be scheduled at the same rate as reading.
       if (base::TimeTicks::Now() < initialization_timeout_) {
-        blocking_task_runner_->PostDelayedTask(
+        ui_task_runner_->PostDelayedTask(
             FROM_HERE,
             base::BindOnce(&AccelerometerFileReader::TryScheduleInitialize,
                            this),