BuiltInFunctionEmulator gets destructed after the PoolAllocator has already
freed memory. That's why BuiltInFunctionEmulator can't hold any objects that
contain parts stored in the memory pool that would be accessed in its
destructor. Use only pointers to TType objects inside
BuiltInFunctionEmulator, so that the BuiltInFunctionEmulator destructor doesn't
access TStrings which have data in the memory pool.

Also fix style issues in BuiltInFunctionEmulator.

BUG=angleproject:1010
TEST=dEQP-GLES3.functional.shaders.builtin_functions.*

Change-Id: Ic35caf80bf125d0427c2ed2024e98657756103b6
Reviewed-on: https://chromium-review.googlesource.com/272738Tested-by: Olli Etuaho <oetuaho@nvidia.com>
Reviewed-by: Zhenyao Mo <zmo@chromium.org>