Turn chrome_public_test_apk to experimental on ansr's dbg CI mirror.

Bug: 833632
Change-Id: I06da0333072b85b1b00f7954f008d39fe3689306
Reviewed-on: https://chromium-review.googlesource.com/1014639Reviewed-by: John Budorick <jbudorick@chromium.org>
Commit-Queue: Ben Pastene <bpastene@chromium.org>
Cr-Commit-Position: refs/heads/master@{#551766}

testing/buildbot/chromium.android.json

@@ -8587,6 +8587,7 @@
           "--gs-results-bucket=chromium-result-details",
           "--recover-devices"
         ],
+        "experiment_percentage": 100,
         "merge": {
           "args": [
             "--bucket",

testing/buildbot/test_suite_exceptions.pyl

@@ -524,6 +524,9 @@
         },
       },
       'Marshmallow 64 bit Tester': {
+        # TODO(crbug.com/731759): Enable this once we're confident that it
+        # passes.
+        'experiment_percentage': 100,
         'swarming': {
           'hard_timeout': 1200,
           'shards': 14,