Linked in parallel, GLSLTest_ES3.LargeNumberOfFloat4Parameters
fails on the Mac asan bots. It looks a driver bug caused by
handling some long GLSL expressions. This works around it by
breaking down the expression in the test from:
    return a0 + a1 + ... + alast;
to:
    vec4 sum = vec4(0, 0, 0, 0);
    sum += a0;
    sum += a1;
    ...
    sum += alast;
    return sum;

This also fixes a CGLPixelFormat leak, although it's irrelevant
to the bot failures.

BUG=922936
BUG=angleproject:3087
BUG=angleproject:3047

Change-Id: I20249ada43e9dd226f582a568ed4ed50a0e4375d
Reviewed-on: https://chromium-review.googlesource.com/c/1426430Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Jie A Chen <jie.a.chen@intel.com>