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

ash/ash_typography.h

Index: ash/ash_typography.h
diff --git a/ash/ash_typography.h b/ash/ash_typography.h
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index 0000000000000000000000000000000000000000..e3017a672b56cd0b06bf40c280cd6646da71a443
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+++ b/ash/ash_typography.h
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+// 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.
+
+#ifndef ASH_COMMON_ASH_TYPOGRAPHY_H_
+#define ASH_COMMON_ASH_TYPOGRAPHY_H_
+
+#include "ash/ash_export.h"
+#include "ui/gfx/font.h"
+#include "ui/views/style/typography.h"
+
+namespace ash {
+
+enum AshTextContext {
+  ASH_TEXT_CONTEXT_START = views::style::VIEWS_TEXT_CONTEXT_END,
+
+  // A button that appears in the launcher's status area.
+  CONTEXT_LAUNCHER_BUTTON = ASH_TEXT_CONTEXT_START,
+
+  // Buttons and labels that appear in the fullscreen toast overlay UI.
+  CONTEXT_TOAST_OVERLAY,
+
+  ASH_TEXT_CONTEXT_END
+};
+
+// Sets the |size_delta| and |font_weight| for ash-specific text contexts.
+// Values are only set for contexts specific to ash.
+void ASH_EXPORT GetDefaultAshFont(int context,
+                                  int style,
+                                  int* size_delta,
+                                  gfx::Font::Weight* font_weight);
+
+}  // namespace ash
+
+#endif  // ASH_COMMON_ASH_TYPOGRAPHY_H_