Bug 1520705 - Enable mochitest-chrome on WebRender r=kats

Enable mochitest-chrome, but skip test_bug331215.xul and test_bug304188.xul because of frequent intermittent failures on WebRener. The intermittent failures already exist and the failure seems not directly related to WebRender implementation.

Differential Revision: https://phabricator.services.mozilla.com/D19115

--HG--
extra : moz-landing-system : lando

taskcluster/ci/test/test-sets.yml

@@ -184,6 +184,7 @@ linux-qr-tests:
     - jsreftest
     - mochitest
     - mochitest-a11y
+    - mochitest-chrome
     - mochitest-gpu
     - mochitest-media
     - mochitest-webgl1-core

toolkit/content/tests/chrome/chrome.ini

@@ -73,8 +73,9 @@ subsuite = clipboard
 [test_bug263683.xul]
 skip-if = debug && (os == 'win' || os == 'linux')
 [test_bug304188.xul]
+skip-if = webrender
 [test_bug331215.xul]
-skip-if = os == 'win' && debug # Bug 1339326
+skip-if = webrender || (os == 'win' && debug) # Bug 1339326
 [test_bug360220.xul]
 [test_bug360437.xul]
 skip-if = os == 'linux' # Bug 1264604