Refactored-out the code of thumbnaling algorithm from thumbnail_tab_helper.

chrome/browser/thumbnails/simple_thumbnail_crop.h

Index: chrome/browser/thumbnails/simple_thumbnail_crop.h
diff --git a/chrome/browser/thumbnails/simple_thumbnail_crop.h b/chrome/browser/thumbnails/simple_thumbnail_crop.h
new file mode 100644
index 0000000000000000000000000000000000000000..472eda75b3b7e3ede4e66c0f16073764b4bf45d7
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+++ b/chrome/browser/thumbnails/simple_thumbnail_crop.h
@@ -0,0 +1,69 @@
+// Copyright (c) 2013 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 CHROME_BROWSER_THUMBNAILS_SIMPLE_THUMBNAIL_CROP_H_
+#define CHROME_BROWSER_THUMBNAILS_SIMPLE_THUMBNAIL_CROP_H_
+
+#include "chrome/browser/thumbnails/thumbnailing_algorithm.h"
+
+namespace thumbnails {
+
+// The implementation of the 'classic' thumbnail cropping algorithm. It is not
+// content-driven in any meaningful way (save for score calculation). Rather,
+// the choice of a cropping region is based on relation between source and
+// target sizes. The selected source region is then rescaled into the target
+// thumbnail image.
+class SimpleThumbnailCrop : public ThumbnailingAlgorithm {
+ public:
+  explicit SimpleThumbnailCrop(const gfx::Size& target_size);
+
+  virtual ClipResult GetCanvasCopyInfo(const gfx::Size& source_size,
+                                       ui::ScaleFactor scale_factor,
+                                       gfx::Rect* clipping_rect,
+                                       gfx::Size* target_size) const OVERRIDE;
+
+  virtual void ProcessBitmap(ThumbnailingContext* context,
+                             const ConsumerCallback& callback,
+                             const SkBitmap& bitmap) OVERRIDE;
+
+  // Calculates how "boring" a thumbnail is. The boring score is the
+  // 0,1 ranged percentage of pixels that are the most common
+  // luma. Higher boring scores indicate that a higher percentage of a
+  // bitmap are all the same brightness.
+  // Statically exposed for use by tests only.
+  static double CalculateBoringScore(const SkBitmap& bitmap);
+
+  // Gets the clipped bitmap from |bitmap| per the aspect ratio of the
+  // desired width and the desired height. For instance, if the input
+  // bitmap is vertically long (ex. 400x900) and the desired size is
+  // square (ex. 100x100), the clipped bitmap will be the top half of the
+  // input bitmap (400x400).
+  // Statically exposed for use by tests only.
+  static SkBitmap GetClippedBitmap(const SkBitmap& bitmap,
+                                   int desired_width,
+                                   int desired_height,
+                                   thumbnails::ClipResult* clip_result);
+  static gfx::Size GetCopySizeForThumbnail(ui::ScaleFactor scale_factor,
+                                           const gfx::Size& thumbnail_size);
+
+ protected:
+  virtual ~SimpleThumbnailCrop();
+
+ private:
+  gfx::Size GetThumbnailSizeInPixel() const;
+  static gfx::Rect GetClippingRect(const gfx::Size& source_size,
+                                   const gfx::Size& desired_size,
+                                   ClipResult* clip_result);
+  static SkBitmap CreateThumbnail(const SkBitmap& bitmap,
+                                  const gfx::Size& desired_size,
+                                  ClipResult* clip_result);
+
+  const gfx::Size target_size_;
+
+  DISALLOW_COPY_AND_ASSIGN(SimpleThumbnailCrop);
+};
+
+}
+
+#endif  // CHROME_BROWSER_THUMBNAILS_SIMPLE_THUMBNAIL_CROP_H_