Rebalance sharding between test suites on marshmallow.

telemetry_perf_unittests currently have the largest amount
of overhead (see bug for measurements). It's double that
of the chrome_public_test_apk and content_browsertests.
Dropping 2 of its shards should allow us to add 4 total
new ones which we split between the other two tests.

Bug: 1021686
Change-Id: I953854770fc5fdb8e45ec9541e535f4ada5fc031
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1918963Reviewed-by: Aaron Gable <agable@chromium.org>
Commit-Queue: Aaron Gable <agable@chromium.org>
Cr-Commit-Position: refs/heads/master@{#715807}

testing/buildbot/chromium.android.json

@@ -26643,7 +26643,7 @@
               "name": "shard #${SHARD_INDEX} logcats"
             }
           ],
-          "shards": 20
+          "shards": 22
         },
         "test": "chrome_public_test_apk"
       },
@@ -26824,7 +26824,7 @@
               "name": "shard #${SHARD_INDEX} logcats"
             }
           ],
-          "shards": 9
+          "shards": 11
         },
         "test": "content_browsertests"
       },
@@ -28859,7 +28859,7 @@
             }
           ],
           "idempotent": false,
-          "shards": 15
+          "shards": 13
         }
       }
     ],

testing/buildbot/test_suite_exceptions.pyl

@@ -316,6 +316,11 @@
       'android-pie-arm64-rel': {
         'experiment_percentage': 100, # https://crbug.com/1010211
       },
+      'android-marshmallow-arm64-rel': {
+        'swarming': {
+          'shards': 22,
+        },
+      },
       'KitKat Phone Tester (dbg)': {
         'swarming': {
           'shards': 20,
@@ -431,6 +436,11 @@
           'shards': 15,
         },
       },
+      'android-marshmallow-arm64-rel': {
+        'swarming': {
+          'shards': 11,
+        },
+      },
       # chromium.linux
       'Cast Audio Linux': {
         'args': [
@@ -1587,7 +1597,7 @@
               'temp_band': '<30',
             },
           ],
-          'shards': 15,
+          'shards': 13,
         },
       },
       'android-pie-arm64-rel': {