Increase Android dEQP-GLES31 test sharding.

The current tests take 16-20 minutes per shard to complete. Given
that these tests are still increasing in time as we add new
features to ANGLE we can double the shard count on Android from
10 to 20.

Bug: angleproject:5323
Change-Id: I313b58576e22ae1fe3d05196e58b5076f6ae137b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2533032Reviewed-by: Yuly Novikov <ynovikov@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Cr-Commit-Position: refs/heads/master@{#826477}

testing/buildbot/chromium.gpu.fyi.json

@@ -2968,7 +2968,7 @@
             }
           ],
           "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com",
-          "shards": 10
+          "shards": 20
         },
         "test": "angle_deqp_gles31_tests",
         "test_id_prefix": "ninja://third_party/angle/src/tests:angle_deqp_gles31_tests/",
@@ -3358,7 +3358,7 @@
             }
           ],
           "service_account": "chromium-tester@chops-service-accounts.iam.gserviceaccount.com",
-          "shards": 10
+          "shards": 20
         },
         "test": "angle_deqp_gles31_tests",
         "test_id_prefix": "ninja://third_party/angle/src/tests:angle_deqp_gles31_tests/",

testing/buildbot/test_suites.pyl

@@ -1886,7 +1886,7 @@
           '--shard-timeout=500',
         ],
         'android_swarming': {
-          'shards': 10,
+          'shards': 20,
         },
         'desktop_args': [
           '--bot-mode',