Specify GYP variable archive_gpu_tests=1 on GPU bots.

scripts/slave/recipes/gpu/build_and_test.expected/mac_debug.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "[BUILD]/scripts/slave/cleanup_temp.py"
     ],
     "name": "cleanup temp"
   },
   {
@@ skipping 98 matching lines @@
     ]
   },
   {
     "cmd": [
       "python",
       "-u",
       "[DEPOT_TOOLS]/gclient.py",
       "runhooks"
     ],
     "env": {
-      "GYP_DEFINES": "blink_asserts_always_on=1 clang=1 component=shared_library dcheck_always_on=1 disable_glibcxx_debug=1 gomadir='[BUILD]/goma' internal_gles2_conform_tests=1 target_arch=ia32 test_isolation_mode=archive test_isolation_outdir=https://isolateserver.appspot.com use_goma=1"
+      "GYP_DEFINES": "archive_gpu_tests=1 blink_asserts_always_on=1 clang=1 component=shared_library dcheck_always_on=1 disable_glibcxx_debug=1 gomadir='[BUILD]/goma' internal_gles2_conform_tests=1 target_arch=ia32 test_isolation_mode=archive test_isolation_outdir=https://isolateserver.appspot.com use_goma=1"
     },
     "name": "gclient runhooks"
   },
   {
     "cmd": [
       "python",
       "-u",
       "[BUILD]/scripts/slave/compile.py",
       "--target",
       "Debug",
@@ skipping 520 matching lines @@
       "[SLAVE_BUILD]/src/tools/swarming_client/run_isolated.py",
       "-H",
       "[dummy hash for tab_capture_end2end_tests]",
       "-I",
       "https://isolateserver.appspot.com",
       "--"
     ],
     "name": "tab_capture_end2end_tests"
   }
 ]