Remove getData from BufferImpl.

We only ever call this method inside the D3D Renderer, so we can
downcast to BufferD3D and call getData on the D3D-specific type.

Leave a FIXME for handling index range validation, which will
need a CPU-side data cache.

Change-Id: Iaf71bc8055869a8561777b6b36f67e376a1d0b81
Reviewed-on: https://chromium-review.googlesource.com/224654
Tested-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Fixed some configuration data not being added to 64-bit builds.

The Debug and Release configurations are 32-bit only.  The Debug_Base and
Release_Base configurations should be used in these cases.

In the future we should not rely on defines being placed in these
configurations because if ANGLE is included in another project, they may
not have the same configuration names and the defines will not be added.
To combat this, always make sure that there are appropriate #ifdef's in
the headers and don't add defines that would result in poor performance if
they do not exist.

BUG=angle:772

Change-Id: I2b26ffb934f8b3d5e6e556a1e87c1c5ee209c430
Reviewed-on: https://chromium-review.googlesource.com/225051
Tested-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>