Enable viz_content_browsertests on Linux CQ

We enabled viz_content_browsertests on the linux fyi bot over the weekend, with
no new flakes nor failures appearing.

This enables them as a part of the main linux test package.

TBR=sky@chromium.org
TEST=viz_content_browsertests

Bug: 760181
Change-Id: If86e8e551bf007124aea88073a3f57b51fff27a3
Reviewed-on: https://chromium-review.googlesource.com/779221Reviewed-by: Jonathan Ross <jonross@chromium.org>
Commit-Queue: Jonathan Ross <jonross@chromium.org>
Cr-Commit-Position: refs/heads/master@{#518338}

testing/buildbot/chromium.linux.json

@@ -3688,6 +3688,18 @@
         },
         "test": "compositor_unittests"
       },
+      {
+        "args": [
+          "--enable-viz",
+          "--test-launcher-filter-file=../../testing/buildbot/filters/viz.content_browsertests.filter"
+        ],
+        "name": "viz_content_browsertests",
+        "swarming": {
+          "can_use_on_swarming_builders": true,
+          "shards": 2
+        },
+        "test": "content_browsertests"
+      },
       {
         "swarming": {
           "can_use_on_swarming_builders": true