RenderTextHarfBuzz: Implement font fallback for Win and Linux

ui/gfx/font_fallback_mac.cc

Index: ui/gfx/font_fallback_mac.cc
diff --git a/ui/gfx/font_fallback_mac.cc b/ui/gfx/font_fallback_mac.cc
new file mode 100644
index 0000000000000000000000000000000000000000..de2937155ef6ca2a6ee51ae25e941d0d99a6d5d6
--- /dev/null
+++ b/ui/gfx/font_fallback_mac.cc
@@ -0,0 +1,15 @@
+// Copyright 2014 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.
+
+#include "ui/gfx/font_fallback.h"
+
+namespace gfx {
+
+std::vector<std::string> GetFallbackFontFamilies(
+    const std::string& font_family) {
+  NOTIMPLEMENTED();
+  return std::vector<std::string>(1, font_family);
+}
+
+}  // namespace gfx