The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/9b8b3e34a3251fba6019857b1299e0bae7892662

commit 9b8b3e34a3251fba6019857b1299e0bae7892662
Author: timvolodine <timvolodine@chromium.org>
Date: Mon May 09 18:58:44 2016

device_sensors: make sure to clear the shared memory buffer on each start.

DataFetcherSharedMemoryBase::StartFetchingDeviceData(ConsumerType)
should clear the shared memory buffer before each start to make
sure there are no stale values.

This patch adds robustness to platform dependent fetcher
implementations e.g. when the buffer is live and its data
is updated incrementally as soon as it becomes available.
It also allows to correctly handle cases when sensors are
disabled or go offline.

BUG= 609533 

Review-Url: https://codereview.chromium.org/1954753002
Cr-Commit-Position: refs/heads/master@{#392386}

[modify] https://crrev.com/9b8b3e34a3251fba6019857b1299e0bae7892662/content/browser/device_sensors/data_fetcher_shared_memory_base.cc
[modify] https://crrev.com/9b8b3e34a3251fba6019857b1299e0bae7892662/content/browser/device_sensors/data_fetcher_shared_memory_base_unittest.cc

old bug, closing