Switched gpumac4 and gpumac5 for build[87,88]-a1.
Switched gpumac4 and gpumac5 for build[87,88]-a1.

This makes the Retina bots on the chromium.gpu waterfall match the
GPUs in the mac_gpu_retina_triggered_tests bot on the
tryserver.chromium.gpu waterfall, and will fix the pixel_tests
failures in the try jobs.

BUG=371194
TBR=iannucci@chromium.org

Review URL: https://codereview.chromium.org/274923002

git-svn-id: 239fca9b83025a0b6f823aeeca02ba5be3d9fd76@269096 0039d316-1c4b-4281-b951-d872f2087c98

eunchong/build,eunchong/build,eunchong/build,eunchong/build