Use the Ahem font to try and deflake DomTreeExtractorBrowserTest

headless/test/data/dom_tree_test.css

Index: headless/test/data/dom_tree_test.css
diff --git a/headless/test/data/dom_tree_test.css b/headless/test/data/dom_tree_test.css
new file mode 100644
index 0000000000000000000000000000000000000000..d2997f47c4bea64726c0568fb95b675718bbbf37
--- /dev/null
+++ b/headless/test/data/dom_tree_test.css
@@ -0,0 +1,21 @@
+/* Copyright 2016 The Chromium Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+@font-face {
+  font-family: 'ahem';
+  src: url(Ahem.ttf);
+}
+
+* {
+  font-family: ahem
+}
+
+.red {
+  color: red;
+}
+
+.green {
+  color: green;
+}