Use 20 shards for chromium.memory browser_tests on win-asan

Rationale: Shards were occassionally timing out (close to completion).
Doubling the number of shards should reduce the number of tests per
shard, making timeouts less likely to happen.

Example failure:
https://ci.chromium.org/p/chromium/builders/ci/win-asan/8793

Bug: 1031096
Test: none
Change-Id: Ic5d1b3029f90c51ff1d73194c720dba7d21bd640
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1950980
Reviewed-by: John Budorick <[email protected]>
Commit-Queue: Pavol Marko <[email protected]>
Cr-Commit-Position: refs/heads/master@{#722258}
diff --git a/testing/buildbot/chromium.memory.json b/testing/buildbot/chromium.memory.json
index ac180cd..9143c34 100644
--- a/testing/buildbot/chromium.memory.json
+++ b/testing/buildbot/chromium.memory.json
@@ -16587,7 +16587,7 @@
               "os": "Windows-10-15063"
             }
           ],
-          "shards": 10
+          "shards": 20
         },
         "test": "browser_tests"
       },
diff --git a/testing/buildbot/test_suite_exceptions.pyl b/testing/buildbot/test_suite_exceptions.pyl
index bd6883fa0..d730dce 100644
--- a/testing/buildbot/test_suite_exceptions.pyl
+++ b/testing/buildbot/test_suite_exceptions.pyl
@@ -265,6 +265,13 @@
           'shards': 15,
         }
       },
+      'win-asan': {
+        # browser_tests shards were reaching a timeout limit of 60 minutes on win-asan
+	# (https://crbug.com/1031096).
+        'swarming': {
+          'shards': 20,
+        },
+      },
       # client.v8.chromium
       'Linux - Future (dbg)': {
         'swarming': {