When an app would load libEGL.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: If3f73fb59dcc5f0713f5b6fb9ca9f8535ee23c73
Reviewed-on: https://chromium-review.googlesource.com/179131Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Geoff Lang <geofflang@chromium.org>
Tested-by: Geoff Lang <geofflang@chromium.org>