Add views::View::set_preferred_size, use it in a few places.

ash/system/tray/fixed_sized_image_view.cc

-// Copyright 2013 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/system/tray/fixed_sized_image_view.h"
-
-namespace ash {
-
-FixedSizedImageView::FixedSizedImageView(int width, int height)
-    : width_(width), height_(height) {}
-
-FixedSizedImageView::~FixedSizedImageView() {}
-
-gfx::Size FixedSizedImageView::GetPreferredSize() const {
-  gfx::Size size = views::ImageView::GetPreferredSize();
-  return gfx::Size(width_ ? width_ : size.width(),
-                   height_ ? height_ : size.height());
-}
-
-}  // namespace ash