Some global initializers depend on other globals, for instance a
varying or attribute value. Since we use a static proxy variable for
these varyings, we need to initialize the global static after we
initialize the proxy in the shader preamble. This fixes a long-
standing compiler bug.

We should also add a WebGL test for this.

BUG=angle:878

Change-Id: I71db103a6b8c24fb862e0d8b32293da9bc2e8103
Reviewed-on: https://chromium-review.googlesource.com/243581Tested-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>