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

ash/common/system/chromeos/session/logout_button_tray.cc

Index: ash/common/system/chromeos/session/logout_button_tray.cc
diff --git a/ash/common/system/chromeos/session/logout_button_tray.cc b/ash/common/system/chromeos/session/logout_button_tray.cc
index 2994b473c61d3e27dcc863e1a81717eda80c2349..5a4eacf06281271f669379fc002df7c3449886e4 100644
--- a/ash/common/system/chromeos/session/logout_button_tray.cc
+++ b/ash/common/system/chromeos/session/logout_button_tray.cc
@@ -7,6 +7,7 @@
 #include <memory>
 #include <utility>
 
+#include "ash/common/ash_typography.h"
 #include "ash/common/shelf/wm_shelf_util.h"
 #include "ash/common/system/chromeos/session/logout_confirmation_controller.h"
 #include "ash/common/system/tray/system_tray_controller.h"
@@ -38,14 +39,10 @@ LogoutButtonTray::LogoutButtonTray(WmShelf* wm_shelf)
       button_(nullptr),
       login_status_(LoginStatus::NOT_LOGGED_IN),
       show_logout_button_in_tray_(false) {
-  views::MdTextButton* button =
-      views::MdTextButton::Create(this, base::string16());
+  views::MdTextButton* button = views::MdTextButton::Create(
+      this, base::string16(), CONTEXT_LAUNCHER_BUTTON);
   button->SetProminent(true);
   button->SetBgColorOverride(gfx::kGoogleRed700);
-  // Base font size + 2 = 14.
-  // TODO(estade): should this 2 be shared with other tray views? See
-  // crbug.com/623987
-  button->AdjustFontSize(2);
   button_ = button;
 
   // Since LogoutButtonTray has a red background and it is distinguished