Disable WebRTC-H264 for viz_content_browsertests on Win10 x64.

Pass --disable-features=WebRTC-H264WithOpenH264FFmpeg to
viz_content_browsertests on "chromium.win:Win10 Tests x64" similarly
to how it's being done for content_browsertests.

Tbr: dpranke@chromium.org
Bug: 867536
Change-Id: Ib04e95a3b1dd94b29027f7cda26b5780e1a16a92
Reviewed-on: https://chromium-review.googlesource.com/1154141Reviewed-by: Kenneth Russell <kbr@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Commit-Queue: Kenneth Russell <kbr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#578901}

testing/buildbot/chromium.win.json

@@ -941,7 +941,8 @@
       },
       {
         "args": [
-          "--enable-features=VizDisplayCompositor"
+          "--enable-features=VizDisplayCompositor",
+          "--disable-features=WebRTC-H264WithOpenH264FFmpeg"
         ],
         "name": "viz_content_browsertests",
         "swarming": {

testing/buildbot/test_suite_exceptions.pyl

@@ -1358,6 +1358,13 @@
           'shards': 7,
         },
       },
+      # chromium.win
+      'Win10 Tests x64': {
+        # crbug.com/868082
+        'args': [
+          '--disable-features=WebRTC-H264WithOpenH264FFmpeg',
+        ],
+      },
     },
   },
   'viz_browser_tests': {