The symbol ids are fetched from the symbol table. A new utility
function is added to make this more convenient.

BUG=angleproject:1490
TEST=angle_unittests, angle_end2end_tests

Change-Id: I780430e3386f6599503d8290c568ca9bc9cad147
Reviewed-on: https://chromium-review.googlesource.com/559535
Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>