Update shelf spacing in Chrome OS according to the MD specs

ash/system/overview/overview_button_tray.h

 // 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.
 
 #ifndef ASH_SYSTEM_OVERVIEW_OVERVIEW_BUTTON_TRAY_H_
 #define ASH_SYSTEM_OVERVIEW_OVERVIEW_BUTTON_TRAY_H_
 
 #include "ash/ash_export.h"
 #include "ash/session/session_state_observer.h"
 #include "ash/shell_observer.h"
@@ skipping 31 matching lines @@
   // ShellObserver:
   void OnMaximizeModeStarted() override;
   void OnMaximizeModeEnded() override;
   void OnOverviewModeEnded() override;
 
   // TrayBackgroundView:
   void ClickedOutsideBubble() override;
   base::string16 GetAccessibleNameForTray() override;
   void HideBubbleWithView(const views::TrayBubbleView* bubble_view) override;
   void SetShelfAlignment(wm::ShelfAlignment alignment) override;
+  void GetHitRegionInsets(gfx::Insets& insets) override;
 
  private:
   friend class OverviewButtonTrayTest;
 
   // Creates a new border for the icon. The padding is determined based on the
   // alignment of the shelf.
   void SetIconBorderForShelfAlignment();
 
   // Sets the icon to visible if maximize mode is enabled and
   // WindowSelectorController::CanSelect.
   void UpdateIconVisibility();
 
   // Weak pointer, will be parented by TrayContainer for its lifetime.
   views::ImageView* icon_;
 
   DISALLOW_COPY_AND_ASSIGN(OverviewButtonTray);
 };
 
 }  // namespace ash
 
 #endif  // ASH_SYSTEM_OVERVIEW_OVERVIEW_BUTTON_TRAY_H_