When an app would load libGLESv2.dll via LoadModule, then would call
methods on a thread that was already created, we could creash because
of uninitialized thread local storage.

BUG=angle:488

Change-Id: I9b05de462232a16d639c58ec07386b7c38a01793
Reviewed-on: https://chromium-review.googlesource.com/179197Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Geoff Lang <geofflang@chromium.org>
Tested-by: Geoff Lang <geofflang@chromium.org>