[Favicon] Add new fallback icon rendering flow.

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..37fb96e2defcc75964eca093888116d9f3f5c75b 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 "ui/gfx/color_utils.h"
 #include "ui/gfx/geometry/size.h"
 #include "ui/gfx/image/image.h"
 #include "url/gurl.h"
@@ -72,6 +73,29 @@ struct FaviconRawBitmapResult {
 // HistoryBackend::SetFavicons().
 typedef FaviconRawBitmapResult FaviconRawBitmapData;
 
+// Rendering specifications of a fallback icon, which is a square image as a
+// solid rounded rectangle containing a single letter. The specs exclude icon
+// URL and size, since these are only specified when we render.
+struct FallbackIconSpecs {
+  FallbackIconSpecs();
+  ~FallbackIconSpecs();
+
+  // Icon background fill color.
+  SkColor background_color;
+
+  // Icon text color.
+  SkColor text_color;
+
+  // Ratio in [0.0, 1.0] from text font size (pixels) to icon size.
+  double font_size_ratio;
+
+  // Ratio in [0.0, 0.5] from rounded square's corner radius to square size.
+  // In particular, 0.0 => square and 0.5 => circle.
+  double corner_radius_ratio;

[pkotwicz, 2015/01/19 04:32:02]

I think that a pixel corner radius is more intuitive (Alternatively you can
rename this member to "roundness". 0.0f -> square, 1.0f -> circle)

[huangs, 2015/01/20 22:20:41]

"Roundness" is a good idea, updating.

+
+  // If any field change, need to update FallbackIconSpecsBuilder.
+};
+
 }  // namespace favicon_base
 
 #endif  // COMPONENTS_FAVICON_BASE_FAVICON_TYPES_H_