[Favicon] Add FallbackIconStyle and FallbackIconService.

components/favicon_base/fallback_icon_style.h

Index: components/favicon_base/fallback_icon_style.h
diff --git a/components/favicon_base/fallback_icon_style.h b/components/favicon_base/fallback_icon_style.h
new file mode 100644
index 0000000000000000000000000000000000000000..097636b0ccb522aacb2af8aaa0612dfe70afe53d
--- /dev/null
+++ b/components/favicon_base/fallback_icon_style.h
@@ -0,0 +1,42 @@
+// 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 {
+  FallbackIconStyle();
+  ~FallbackIconStyle();
+
+  // If any member changes, also update FallbackIconStyleBuilder.
+
+  // 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;
+};
+
+// Reassigns |style|'s |text_color| to matches well against |background_color|.
+void MatchFallbackIconTextColorAgainstBackgroundColor(FallbackIconStyle* style);
+
+// Returns whether |style| values are within bounds.
+bool ValidateFallbackIconStyle(const FallbackIconStyle& style);

[stevenjb, 2015/02/11 21:15:58]

FWIW I think this would have been better as a class with accessors, but this is
fine.

[huangs, 2015/02/11 21:21:56]

Acknowledged.

+
+}  // namespace favicon_base
+
+#endif  // COMPONENTS_FAVICON_BASE_FALLBACK_ICON_STYLE_H_