This is a reland of dc7bffd0

Reland fixes the memory regression by not calling new, instead
calling the pool allocator directly.

Original change's description:
> Make TType store a const char * for mangled name.
>
> We would only ever use the c_str value from the mangled name. This
> makes it easier to make constexpr TTypes.
>
> Bug: angleproject:1432
> Change-Id: I147b3a85f9b8b2453e2d7f4a713d767b22036cc9
> Reviewed-on: https://chromium-review.googlesource.com/776277
> Commit-Queue: Jamie Madill <jmadill@chromium.org>
> Reviewed-by: Kai Ninomiya <kainino@chromium.org>

Bug: angleproject:1432
Change-Id: I1aaeea883186b9061955d55f2fa77d27f5d9b725
Reviewed-on: https://chromium-review.googlesource.com/782406Reviewed-by: Kai Ninomiya <kainino@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>