Reland "Run browser_tests as a 25% experiment on Mac10.13 Tests & mac_chromium_rel_ng."

This reverts commit b41baee6.

Reason for revert: we believe browser_tests are now stable

Original change's description:
> Revert "Run browser_tests as a 25% experiment on Mac10.13 Tests & mac_chromium_rel_ng."
> 
> This reverts commit b20ba21c.
> 
> Reason for revert: Added capacity isn't finding bot deaths as fast as manual, targeted swarming invocations. Will reland this after having some confidence that the 10.13 bot-killer tests are identified.
> 
> Original change's description:
> > Run browser_tests as a 25% experiment on Mac10.13 Tests & mac_chromium_rel_ng.
> > 
> > Bug: 828031
> > Change-Id: I1d4bdb235ad9d93df0653215c7c5928c471b6c16
> > Reviewed-on: https://chromium-review.googlesource.com/c/1277693
> > Reviewed-by: Robert Sesek <rsesek@chromium.org>
> > Commit-Queue: John Budorick <jbudorick@chromium.org>
> > Cr-Commit-Position: refs/heads/master@{#599364}
> 
> TBR=rsesek@chromium.org,jbudorick@chromium.org
> 
> # Not skipping CQ checks because original CL landed > 1 day ago.
> 
> Bug: 828031
> Change-Id: I38c447f53d533eeff40abfd462c3bb1f09eac75f
> Reviewed-on: https://chromium-review.googlesource.com/c/1282283
> Reviewed-by: Robert Sesek <rsesek@chromium.org>
> Reviewed-by: John Budorick <jbudorick@chromium.org>
> Commit-Queue: Robert Sesek <rsesek@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#599869}

TBR=rsesek@chromium.org,jbudorick@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 828031
Change-Id: I297bdbf59e21ebf50aad80f97f7d3aad83e4ccb7
Reviewed-on: https://chromium-review.googlesource.com/c/1287311
Commit-Queue: Robert Sesek <rsesek@chromium.org>
Reviewed-by: Robert Sesek <rsesek@chromium.org>
Reviewed-by: John Budorick <jbudorick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#600841}

testing/buildbot/chromium.mac.json

@@ -3645,6 +3645,25 @@
         },
         "test": "boringssl_ssl_tests"
       },
+      {
+        "args": [
+          "--test-launcher-filter-file=../../testing/buildbot/filters/mac_window_server_killers.browser_tests.filter",
+          "--gtest_shuffle"
+        ],
+        "experiment_percentage": 25,
+        "swarming": {
+          "can_use_on_swarming_builders": true,
+          "dimension_sets": [
+            {
+              "gpu": "none",
+              "os": "Mac-10.13",
+              "pool": "Chrome-quarantine"
+            }
+          ],
+          "shards": 10
+        },
+        "test": "browser_tests"
+      },
       {
         "args": [
           "--enable-features=WebUIPolymer2",

testing/buildbot/test_suite_exceptions.pyl

@@ -75,7 +75,6 @@
       'mac-views-rel', # https://crbug.com/828031
       # chromium.mac
       'Mac10.10 Tests', # https://crbug.com/828031
-      'Mac10.13 Tests', # https://crbug.com/828031
       # chromium.memory
       'Linux TSan Tests',  # https://crbug.com/368525
       'Mac ASan 64 Tests (1)', # https://crbug.com/828031
@@ -133,6 +132,23 @@
           ],
         },
       },
+      'Mac10.13 Tests': {
+        # A subset of tests seem to cause WindowServer deaths on VMs.
+        # crbug.com/828031 et al.
+        'args': [
+          '--test-launcher-filter-file=../../testing/buildbot/filters/mac_window_server_killers.browser_tests.filter',
+          '--gtest_shuffle',
+        ],
+        'experiment_percentage': 25,
+        'swarming': {
+          'dimension_sets': [
+            {
+              'pool': 'Chrome-quarantine',
+              'gpu': 'none',
+            },
+          ],
+        },
+      },
       'Mac10.13 Tests (dbg)': {
         # A subset of tests seem to cause WindowServer deaths on VMs.
         # crbug.com/828031 et al.