Use GPU for layout tests on KitKat Phone Tester (dbg).

SwiftShader isn't available on 32-bit ARM yet.

Bug: 875172
Change-Id: I3ddeec51d8ef156def5f5194c75cec31a4aa9412
Reviewed-on: https://chromium-review.googlesource.com/1181767Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Reviewed-by: John Budorick <jbudorick@chromium.org>
Commit-Queue: Kenneth Russell <kbr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#584563}

testing/buildbot/chromium.android.json

@@ -3157,7 +3157,8 @@
       {
         "args": [
           "--debug",
-          "--android"
+          "--android",
+          "--use-gpu-in-tests"
         ],
         "experiment_percentage": 100,
         "isolate_name": "webkit_layout_tests_exparchive",

testing/buildbot/test_suite_exceptions.pyl

@@ -1471,6 +1471,9 @@
         'args': [
           '--debug',
           '--android',
+          # TODO(crbug.com/875172): run on the real GPU since the
+          # software fallback, SwiftShader, isn't yet for 32-bit ARM.
+          '--use-gpu-in-tests',
         ],
         'experiment_percentage': 100, # crbug.com/824539
       },