Add persistent_shell experiment to content_browsertests.

Adding experiment for content browsertet for android-pie-arm64-rel and
android-nougat-x86-rel.

Bug: 1239300
Change-Id: I763fae179e3133ff7825d3f1244ddb1e48bb48e0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3984965
Reviewed-by: Haiyang Pan <[email protected]>
Commit-Queue: Benjamin Joyce (Ben) <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1064097}
diff --git a/testing/buildbot/test_suite_exceptions.pyl b/testing/buildbot/test_suite_exceptions.pyl
index db703e1a..b477ce1 100644
--- a/testing/buildbot/test_suite_exceptions.pyl
+++ b/testing/buildbot/test_suite_exceptions.pyl
@@ -1822,6 +1822,24 @@
       },
     },
   },
+  # TODO(crbug/1239300): Remove when experiment is done.
+  'content_browsertests_persistent_shell': {
+    'modifications': {
+      'android-nougat-x86-rel': {
+        'args': [
+          '--test-launcher-filter-file=../../testing/buildbot/filters/android.emulator_n.content_browsertests.filter',
+        ],
+        'swarming': {
+          'shards': 25,
+          'dimension_sets': [
+            {
+              'machine_type': 'e2-standard-8', # copying android-nougat-x86-rel
+            },
+          ],
+        },
+      },
+    },
+  },
   'content_shell_crash_test': {
     'remove_from': [
       'android-nougat-x86-rel', # crbug.com/1084353