[ash-md] Wired in the Shelf color to be derived from the Wallpaper.

components/wallpaper/wallpaper_color_calculator.h

+// Copyright 2017 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_WALLPAPER_WALLPAPER_COLOR_CALCULATOR_H_
+#define COMPONENTS_WALLPAPER_WALLPAPER_COLOR_CALCULATOR_H_
+
+#include "base/macros.h"
+#include "base/memory/ref_counted.h"
+#include "base/memory/weak_ptr.h"
+#include "base/observer_list.h"
+#include "base/time/time.h"
+#include "components/wallpaper/wallpaper_color_calculator_observer.h"
+#include "components/wallpaper/wallpaper_export.h"
+#include "third_party/skia/include/core/SkColor.h"
+#include "ui/gfx/color_analysis.h"
+#include "ui/gfx/image/image_skia.h"
+
+namespace base {
+class TaskRunner;
+}
+
+namespace wallpaper {
+class WallpaperColorCalculatorObserver;
+
+// Asynchronously calculates colors based on a wallpaper image.
+class WALLPAPER_EXPORT WallpaperColorCalculator {
+ public:
+  // |image|, |luma| and |saturation| are the input parameters to the color
+  // calculation that is executed on the |task_runner|.
+  WallpaperColorCalculator(const gfx::ImageSkia& image,
+                           color_utils::LumaRange luma,
+                           color_utils::SaturationRange saturation,
+                           scoped_refptr<base::TaskRunner> task_runner);
+  ~WallpaperColorCalculator();
+
+  void AddObserver(WallpaperColorCalculatorObserver* observer);
+
+  void RemoveObserver(WallpaperColorCalculatorObserver* observer);
+
+  // Initiates the calculation and returns false if the calculation fails to be
+  // initiated.  Callers should be aware that this will make |image_| read-only.
+  bool StartCalculation() WARN_UNUSED_RESULT;
+
+  SkColor prominent_color() const { return prominent_color_; }
+
+  void set_prominent_color_for_test(SkColor prominent_color) {
+    prominent_color_ = prominent_color;
+  }
+
+  // Explicitly sets the |task_runner_| for testing.
+  void SetTaskRunnerForTest(scoped_refptr<base::TaskRunner> task_runner);
+
+ private:
+  // Notifies observers that a color calulation has completed. Called on the
+  // same thread that constructed |this|.
+  void NotifyCalculationComplete(SkColor prominent_color);
+
+  // The result of the color calculation.
+  SkColor prominent_color_ = SK_ColorTRANSPARENT;
+
+  // The image to calculate colors from.
+  gfx::ImageSkia image_;
+
+  // Input for the color calculation.
+  color_utils::LumaRange luma_;
+
+  // Input for the color calculation.
+  color_utils::SaturationRange saturation_;
+
+  // The task runner to run the calculation on.
+  scoped_refptr<base::TaskRunner> task_runner_;
+
+  // The time that StartCalculation() was last called. Used for recording
+  // timing metrics.
+  base::Time start_calculation_time_;
+
+  base::ObserverList<WallpaperColorCalculatorObserver> observers_;
+
+  base::WeakPtrFactory<WallpaperColorCalculator> weak_ptr_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(WallpaperColorCalculator);
+};
+
+}  // namespace wallpaper
+
+#endif  // COMPONENTS_WALLPAPER_WALLPAPER_COLOR_CALCULATOR_H_