Run Linux and Win ANGLE trybots during WebGL conformance rolls.

This will help prevent breakage of the ANGLE CQ by running currently
non-default configurations.

BUG=none
TBR=jmadill@chromium.org
NOTRY=true

Change-Id: Ib49f1a0911f7a1430f6dc513fea4573c5720a8b0
Reviewed-on: https://chromium-review.googlesource.com/808089
Commit-Queue: Kenneth Russell <kbr@chromium.org>
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#521645}

tools/roll_webgl_conformance.py

@@ -29,6 +29,16 @@ extra_trybots = [
     "mastername": "master.tryserver.chromium.android",
     "buildernames": ["android_optional_gpu_tests_rel"]
   },
+  # Include the ANGLE tryservers which run the WebGL conformance tests
+  # in some non-default configurations.
+  {
+    "mastername": "master.tryserver.chromium.angle",
+    "buildernames": ["linux_angle_rel_ng"]
+  },
+  {
+    "mastername": "master.tryserver.chromium.angle",
+    "buildernames": ["win_angle_rel_ng"]
+  },
 ]
 
 SCRIPT_DIR = os.path.dirname(os.path.realpath(__file__))