[Favicon] Add FallbackIconStyle and FallbackIconService.

components/favicon_base/favicon_types.h

Index: components/favicon_base/favicon_types.h
diff --git a/components/favicon_base/favicon_types.h b/components/favicon_base/favicon_types.h
index ea6475429d93d931fb9f511fbe24adaa16ccd38e..7b3a4f7ad32babd27e13cfdfd5ff4c7ffa10b0a6 100644
--- a/components/favicon_base/favicon_types.h
+++ b/components/favicon_base/favicon_types.h
@@ -6,6 +6,7 @@
 #define COMPONENTS_FAVICON_BASE_FAVICON_TYPES_H_
 
 #include "base/memory/ref_counted_memory.h"
+#include "third_party/skia/include/core/SkColor.h"
 #include "ui/gfx/geometry/size.h"
 #include "ui/gfx/image/image.h"
 #include "url/gurl.h"
@@ -72,6 +73,34 @@ struct FaviconRawBitmapResult {
 // HistoryBackend::SetFavicons().
 typedef FaviconRawBitmapResult FaviconRawBitmapData;
 
+// 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();
+
+  // 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_FAVICON_TYPES_H_