Fix race condition in DataFetcherSharedMemoryBase

Fix race condition in DataFetcherSharedMemoryBase

A race condition can occur when a polling thread tries to obtain a pointer to the shared memory via a std::map, while that map is modified by the main thread.
This patch implements a fix such that the polling thread does not have direct access to the std::map where the shared memory pointers are stored. Instead the pointer is passed as an argument of the Start() method.

This patch fixes the DataFetcherSharedMemoryBaseTest.DoesPollMotionAndOrientation test on linux tsan.

BUG=284959
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=221404

[timvolodine, 2013-09-04 16:36:17]

+ bruening@
for tools/valgrind/tsan/suppressions.txt

[bulach, 2013-09-04 16:51:45]

wow, great catch! lgtm, thanks!

[timvolodine, 2013-09-05 10:36:52]

+ timurrrr@
(as Derek seems to be OOO)

[Alexander Potapenko, 2013-09-05 10:40:54]

On 2013/09/05 10:36:52, timvolodine wrote:
> + timurrrr@
> (as Derek seems to be OOO)
Suppression file LGTM

[commit-bot: I haz the power, 2013-09-05 10:43:39]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/timvolodine@chromium.org/23441047/1

[Timur Iskhodzhanov, 2013-09-05 11:05:19]

2013/9/5 <timvolodine@chromium.org>

> + timurrrr@
> (as Derek seems to be OOO)
>

FYI you don't need an owner review for removing suppressions

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[commit-bot: I haz the power, 2013-09-05 13:25:04]

Change committed as 221404