Refactored-out the code of thumbnaling algorithm from thumbnail_tab_helper.

chrome/browser/thumbnails/thumbnailing_context.h

+// 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_THUMBNAILING_CONTEXT_H_
+#define CHROME_BROWSER_THUMBNAILS_THUMBNAILING_CONTEXT_H_
+
+#include "base/basictypes.h"
+#include "base/memory/ref_counted.h"
+#include "chrome/common/thumbnail_score.h"
+#include "content/public/browser/web_contents.h"
+
+namespace thumbnails {
+
+// The result of clipping. This can be used to determine if the
+// generated thumbnail is good or not.
+enum ClipResult {
+  // Clipping is not done yet.
+  kUnprocessed,

[sky, 2013/01/17 20:18:36]

chrome style is enums should be CAPS_CASE.

[motek., 2013/01/18 18:38:41]

Done.

+  // The source image is smaller.
+  kSourceIsSmaller,
+  // Wider than tall by twice or more, clip horizontally.
+  kTooWiderThanTall,
+  // Wider than tall, clip horizontally.
+  kWiderThanTall,
+  // Taller than wide, clip vertically.
+  kTallerThanWide,
+  // The source and destination aspect ratios are identical.
+  kNotClipped,
+};
+
+// Holds the information needed for processing a thumbnail.
+struct ThumbnailingContext : base::RefCountedThreadSafe<ThumbnailingContext> {

[sky, 2013/01/17 20:18:36]

Why does this need to be RefCountedThreadSafe? If you are passing this to a
different thread, don't pass around BrowserContext.

[motek., 2013/01/18 18:38:41]

Right. I copied it from elsewhere, without thinking much. I believe that it
could have been indeed passed between threads, but it would have always ended in
BrowserThread::UI whenever used. It is declared as RefCountedThreadSafe in its
current form (see present thumbnail_tab_helper.h).
Turns out in the end BrowserContext is not really needed. Replaced that with
ThumbnailingService.

+  ThumbnailingContext(content::WebContents* web_contents,
+                      bool load_interrupted);
+
+  content::BrowserContext* browser_context;
+  GURL url;
+  ClipResult clip_result;
+  ThumbnailScore score;
+
+ private:
+  ~ThumbnailingContext();
+  friend class base::RefCountedThreadSafe<ThumbnailingContext>;
+};
+
+}
+
+#endif  // CHROME_BROWSER_THUMBNAILS_THUMBNAILING_CONTEXT_H_