[Favicon] Add FallbackIconStyle and FallbackIconService.

Design: go/chrome-fallback-icons

This implements
- FallbackIconStyle: A struct to specify fallback data.
- FallbackIconService: Helper class to render the fallback icon as a
  filled rounded square with a single letter from the URL.
- Extra dependencies are needed to convert URL to the icon letter.

This CL is sliced off from https://codereview.chromium.org/835903005/ .

BUG=455063

Review URL: https://codereview.chromium.org/886163003

Cr-Commit-Position: refs/heads/master@{#315854}

1 files changed, 48 insertions, 0 deletions

diff --git a/components/favicon_base/fallback_icon_style.cc b/components/favicon_base/fallback_icon_style.cc
new file mode 100644
index 0000000..e620613
--- /dev/null
+++ b/components/favicon_base/fallback_icon_style.cc
@@ -0,0 +1,48 @@
+// 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.
+
+#include "components/favicon_base/fallback_icon_style.h"
+
+#include "ui/gfx/color_utils.h"
+
+namespace favicon_base {
+
+namespace {
+
+// Luminance threshold for background color determine whether to use dark or
+// light text color.
+int kDarkTextLuminanceThreshold = 190;
+
+// Default values for FallbackIconStyle.
+SkColor kDefaultBackgroundColor = SkColorSetRGB(0x80, 0x80, 0x80);
+SkColor kDefaultTextColorDark = SK_ColorBLACK;
+SkColor kDefaultTextColorLight = SK_ColorWHITE;
+double kDefaultFontSizeRatio = 0.8;
+double kDefaultRoundness = 0.125;  // 1 / 8.
+
+}  // namespace
+
+FallbackIconStyle::FallbackIconStyle()
+    : background_color(kDefaultBackgroundColor),
+      text_color(kDefaultTextColorLight),
+      font_size_ratio(kDefaultFontSizeRatio),
+      roundness(kDefaultRoundness) {
+}
+
+FallbackIconStyle::~FallbackIconStyle() {
+}
+
+void MatchFallbackIconTextColorAgainstBackgroundColor(
+    FallbackIconStyle* style) {
+  int luminance = color_utils::GetLuminanceForColor(style->background_color);
+  style->text_color = (luminance >= kDarkTextLuminanceThreshold ?
+      kDefaultTextColorDark : kDefaultTextColorLight);
+}
+
+bool ValidateFallbackIconStyle(const FallbackIconStyle& style) {
+  return style.font_size_ratio >= 0.0 && style.font_size_ratio <= 1.0 &&
+      style.roundness >= 0.0 && style.roundness <= 1.0;
+}
+
+}  // namespace favicon_base