DM: only depend on GpuTest when it's a GPU build.

This seems to fix DM dynamic linking errors on IntelRHB.

Not clear why this device is the only one with this problem.  It does set
skia_gpu=0, but I can't reproduce the same failure on my desktop (skia_gpu=0,
skia_shared_lib=1, skia_arch_width=32).

BUG=skia:
R=bsalomon@google.com, mtklein@google.com

Author: mtklein@chromium.org

Review URL: https://codereview.chromium.org/435673002
1 file changed