[Favicon] Add new fallback icon rendering flow.

components/favicon_base/fallback_icon_style_builder.h

Index: components/favicon_base/fallback_icon_style_builder.h
diff --git a/components/favicon_base/fallback_icon_style_builder.h b/components/favicon_base/fallback_icon_style_builder.h
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+++ b/components/favicon_base/fallback_icon_style_builder.h
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+// 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_BUILDER_H_
+#define COMPONENTS_FAVICON_BASE_FALLBACK_ICON_STYLE_BUILDER_H_
+
+#include <memory>
+#include <string>
+
+#include "base/logging.h"
+#include "base/macros.h"
+#include "components/favicon_base/favicon_types.h"
+#include "third_party/skia/include/core/SkColor.h"
+
+namespace favicon_base {
+
+// Helper to initialize FallbackIconStyle. A caller can specify values for data
+// members, then call Build() to assign defaults for missing values, and return
+// an intance of FallbackIconStyle. Validated parsing from a specification
+// string is also supported.
+class FallbackIconStyleBuilder {
+ public:
+  // One member for each element in FallbackIconStyle.
+  enum DataMember {
+    BACKGROUND_COLOR = 1 << 0,
+    TEXT_COLOR = 1 << 1,
+    FONT_SIZE_RATIO = 1 << 2,
+    ROUNDNESS = 1 << 3,
+  };
+
+  FallbackIconStyleBuilder();
+  ~FallbackIconStyleBuilder();
+
+  // Clear all data members and returns false.
+  bool Reset();
+
+  // Determines whether a given data member is initialized.
+  bool Has(DataMember mask) const;
+
+  // Setters, which does not validate |value|.
+  void SetBackgroundColor(SkColor value);
+
+  void SetTextColor(SkColor value);
+
+  void SetFontSizeRatio(double value);
+
+  void SetRoundness(double value);
+
+  // Parses |str| as |RRGGBBAA|, |RRGGBB|, or |RGB| hex color, no leading '#'.
+  // Returns true and writes to |color| on success.
+  static bool ParseColor(const std::string& str, SkColor* color);
+
+  // Parses a comma-separated list of specification string and populates
+  // relevent fields. If parse is successful, returns true. Otherwise clear all
+  // fields and return false.
+  // Specification string is:
+  //   <background_color>,<text_color>,<font_size_ratio>,<corner_radius_ratio>
+  // where:
+  //   <background_color> Is color in RRGBBBAA, RRGGBB, or RGB hex format,
+  //   <text_color> Is color in RRGBBBAA, RRGGBB, or RGB hex format,
+  //   <font_size_ratio> Is a double in [0.0, 1.0].
+  //   <corner_radius_ratio> Is a double in [0.0, 0.5].
+  // Fields are optional.
+  bool Parse(const std::string& specs_str);
+
+  // Initializes all data members to default values. These are all constants,
+  // except |text_color_|, which is adjusted based on the |background_color_|
+  // luminance so it can be seen.
+  void AssignDefaults();
+
+  // Assigns defaults if necessary, and returns const ref to |specs_|.
+  const FallbackIconStyle& Build();
+
+ private:
+  // A bit mask (over DataMember) to store intialization states of data members.
+  unsigned int is_init_;
+
+  // Storage of data members.
+  FallbackIconStyle specs_;
+
+  DISALLOW_COPY_AND_ASSIGN(FallbackIconStyleBuilder);
+};
+
+}  // namespace favicon_base
+
+#endif  // COMPONENTS_FAVICON_BASE_FALLBACK_ICON_STYLE_BUILDER_H_