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The C++ thread_local is slightly faster while making the code clear.
Besides that calls to TlsGetValue on Windows may alter the result of
GetLastError, thus changing behavior of the underlying code.

BUG=920440

Change-Id: Ic89632f4a54f35d58b93cdecfffc68fc1a94dac1
Reviewed-on: https://chromium-review.googlesource.com/c/1461681Reviewed-by: Vlad Tsyrklevich <vtsyrklevich@chromium.org>
Reviewed-by: Erik Chen <erikchen@chromium.org>
Commit-Queue: Alexei Filippov <alph@chromium.org>
Cr-Commit-Position: refs/heads/master@{#632819}