Filter -SmsServiceTest.RecordMetricsFor{NewExisting}Page on bfcache bots.

These tests are newly added and failing.

Bug: 1029248
Change-Id: I5d9860183de06b876d76a87de06badfd31c4179d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1941647Reviewed-by: Hajime Hoshi <hajimehoshi@chromium.org>
Commit-Queue: Fergal Daly <fergal@chromium.org>
Cr-Commit-Position: refs/heads/master@{#719901}

testing/buildbot/filters/bfcache.content_unittests.filter

 # These tests currently fail when run with --enable-features=BackForwardCache
+
+# https://crbug.com/1029248
+# Need investigation.
+-SmsServiceTest.RecordMetricsForNewPage
+-SmsServiceTest.RecordMetricsForExistingPage