[Favicon] Add FallbackIconStyle and FallbackIconService.

components/favicon_base/fallback_icon_style.h

+// Copyright 2015 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 COMPONENTS_FAVICON_BASE_FALLBACK_ICON_STYLE_H_
+#define COMPONENTS_FAVICON_BASE_FALLBACK_ICON_STYLE_H_
+
+#include "third_party/skia/include/core/SkColor.h"
+
+namespace favicon_base {
+
+// Styling specifications of a fallback icon. The icon is composed of a solid
+// rounded square containing a single letter. The specification excludes the
+// icon URL and size, which are given when the icon is rendered.
+struct FallbackIconStyle {

[stevenjb, 2015/02/11 18:04:37]

From the style guide: "Use a struct only for passive objects that carry data;
everything else is a class."

[huangs, 2015/02/11 20:28:39]

I want the ability to directly access member variables.

Changing the member functions to helper utilities in favicon_base.

+  FallbackIconStyle();
+  ~FallbackIconStyle();
+
+  // Reassigns |text_color| so it matches well with |background_color|.
+  void MatchTextColorWithBackgroundColor();
+
+  // If any member changes, also update FallbackIconStyleBuilder.
+
+  // Returns true if values stored are within bounds.
+  bool is_valid() const;
+
+  // Icon background fill color.
+  SkColor background_color;
+
+  // Icon text color.
+  SkColor text_color;
+
+  // Ratio in [0.0, 1.0] of the text font size (pixels) to the icon size.
+  double font_size_ratio;
+
+  // The roundness of the icon's corners. 0 => square icon, 1 => circle icon.
+  double roundness;
+};
+
+}  // namespace favicon_base
+
+#endif  // COMPONENTS_FAVICON_BASE_FALLBACK_ICON_STYLE_H_