Enable ViewsBrowserWindows for the tests running on mac-views-rel

Bug: 826341
Change-Id: Ifd2630580efceffab3b73e617e031c32a3a1be13
Reviewed-on: https://chromium-review.googlesource.com/1040947
Commit-Queue: Lindsay Pasricha <lindsayw@chromium.org>
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Cr-Commit-Position: refs/heads/master@{#556110}

testing/buildbot/waterfalls.pyl

@@ -918,6 +918,9 @@
         'test_suites': {
           'gtest_tests': 'chromium_mac_fyi_gtests',
         },
+        'args': [
+          '--enable-features=ViewsBrowserWindows',
+        ],
       },
       'Chromium Mac 10.11': {
         'test_suites': {