android: Have content_browsertests running on 100% on android-pie-arm64-rel

The crrev.com/c/2534602 which adds it as 50% does not seem to affect
the build duration a lot: http://shortn/_lvbjprI51m.
And there are still plenty of test devices: http://shortn/_ZtBguxAg9X

Bug: 1111436
Change-Id: I0126df515488a5241e0a91aac8122bf21d66391f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2541222Reviewed-by: Stephen Martinis <martiniss@chromium.org>
Commit-Queue: Haiyang Pan <hypan@google.com>
Cr-Commit-Position: refs/heads/master@{#827932}

testing/buildbot/chromium.android.json

@@ -39149,7 +39149,7 @@
           "--gs-results-bucket=chromium-result-details",
           "--recover-devices"
         ],
-        "experiment_percentage": 50,
+        "experiment_percentage": 100,
         "merge": {
           "args": [
             "--bucket",

testing/buildbot/test_suite_exceptions.pyl

@@ -1059,7 +1059,7 @@
         ],
       },
       'android-pie-arm64-rel': {
-        'experiment_percentage': 50,
+        'experiment_percentage': 100,
       },
       'android-pie-x86-rel': {
         'args': [