views: Make view::Views::GetPreferredSize() const.

ash/system/chromeos/virtual_keyboard/virtual_keyboard_tray.cc

Index: ash/system/chromeos/virtual_keyboard/virtual_keyboard_tray.cc
diff --git a/ash/system/chromeos/virtual_keyboard/virtual_keyboard_tray.cc b/ash/system/chromeos/virtual_keyboard/virtual_keyboard_tray.cc
index 2875d9ed9d7e399874e94778049efc8a96a8bc51..88d74c4e7cab67a1ee84396e2350dda59cb2634c 100644
--- a/ash/system/chromeos/virtual_keyboard/virtual_keyboard_tray.cc
+++ b/ash/system/chromeos/virtual_keyboard/virtual_keyboard_tray.cc
@@ -28,7 +28,7 @@ class VirtualKeyboardButton : public views::ImageButton {
   virtual ~VirtualKeyboardButton();
 
   // Overridden from views::ImageButton:
-  virtual gfx::Size GetPreferredSize() OVERRIDE;
+  virtual gfx::Size GetPreferredSize() const OVERRIDE;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(VirtualKeyboardButton);
@@ -41,7 +41,7 @@ VirtualKeyboardButton::VirtualKeyboardButton(views::ButtonListener* listener)
 VirtualKeyboardButton::~VirtualKeyboardButton() {
 }
 
-gfx::Size VirtualKeyboardButton::GetPreferredSize() {
+gfx::Size VirtualKeyboardButton::GetPreferredSize() const {
   const int virtual_keyboard_button_height = kShelfSize;
   gfx::Size size = ImageButton::GetPreferredSize();
   int padding = virtual_keyboard_button_height - size.height();