Use views::style for buttons, bootstrap ash_typography to do so.

ash/common/ash_typography.cc

Index: ash/common/ash_typography.cc
diff --git a/ash/common/ash_typography.cc b/ash/common/ash_typography.cc
new file mode 100644
index 0000000000000000000000000000000000000000..a18b813efe8820f57373ef509514f51fb2604837
--- /dev/null
+++ b/ash/common/ash_typography.cc
@@ -0,0 +1,23 @@
+// Copyright 2017 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 "ash/common/ash_typography.h"
+
+namespace ash {
+
+void GetDefaultAshFont(int context,
+                       int style,
+                       int* size_delta,
+                       gfx::Font::Weight* font_weight) {
+  switch (context) {
+    case CONTEXT_LAUNCHER_BUTTON:
+      *size_delta = 2;
+      break;
+    case CONTEXT_TOAST_OVERLAY:
+      *size_delta = 3;
+      break;
+  }
+}
+
+}  // namespace ash