Bug 1507532 - Set up mach defaults to match working wpt android reftest settings, r=KWierso

The fast internal reftest harness doesn't work yet, so in the meantime
default to the functional but slower external harness. Also ensure
that the Ahem font is installed by default.

Depends on D12035

Differential Revision: https://phabricator.services.mozilla.com/D12036

testing/web-platform/mach_commands.py

@@ -47,6 +47,12 @@ class WebPlatformTestsRunnerSetup(MozbuildObject):
             if kwargs["certutil_binary"] is None:
                 kwargs["certutil_binary"] = os.path.join(os.environ.get('MOZ_HOST_BIN'), "certutil")
 
+            if kwargs["install_fonts"] is None:
+                kwargs["install_fonts"] = True
+
+            if kwargs["reftest_internal"] is None:
+                kwargs["reftest_internal"] = False
+
         if kwargs["config"] is None:
             kwargs["config"] = os.path.join(self.topobjdir, '_tests', 'web-platform', 'wptrunner.local.ini')