Increase sharding for sync_integration_tests on linux ASAN builder.

The test suite takes 27 minutes to run with only 40 seconds overhead. It's the
slowest test suite on linux_chromium_asan_rel_ng, which causes long cycle times.

Bug: 1028289
Change-Id: Ib82100928d89e29747a8794f62eccc09cf27aae3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1932475
Commit-Queue: Erik Chen <erikchen@chromium.org>
Commit-Queue: John Budorick <jbudorick@chromium.org>
Auto-Submit: Erik Chen <erikchen@chromium.org>
Reviewed-by: John Budorick <jbudorick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#718886}

testing/buildbot/chromium.memory.json

@@ -4403,7 +4403,8 @@
             {
               "os": "Ubuntu-16.04"
             }
-          ]
+          ],
+          "shards": 4
         },
         "test": "sync_integration_tests"
       },

testing/buildbot/test_suite_exceptions.pyl

@@ -1550,6 +1550,12 @@
         },
       },
       # chromium.memory
+      'Linux ASan LSan Tests (1)': {
+        'swarming': {
+          'shards': 4,
+        },
+      },
+      # chromium.memory
       'Linux TSan Tests': {
         'swarming': {
           'shards': 6,