Adds kind-of-live thumbnail generation for a potential tab switcher.

chrome/browser/tab_contents/thumbnail_generator.h

Index: chrome/browser/tab_contents/thumbnail_generator.h
diff --git a/chrome/browser/tab_contents/thumbnail_generator.h b/chrome/browser/tab_contents/thumbnail_generator.h
new file mode 100755
index 0000000000000000000000000000000000000000..76afb3c44fc7377efe98a789c69acbcc94eceaad
--- /dev/null
+++ b/chrome/browser/tab_contents/thumbnail_generator.h
@@ -0,0 +1,75 @@
+// Copyright (c) 2009 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_TAB_CONTENTS_THUMBNAIL_GENERATOR_H_
+#define CHROME_BROWSER_TAB_CONTENTS_THUMBNAIL_GENERATOR_H_
+
+#include "base/basictypes.h"
+#include "base/timer.h"
+#include "chrome/browser/renderer_host/render_widget_host_painting_observer.h"
+#include "chrome/common/notification_observer.h"
+#include "chrome/common/notification_registrar.h"
+
+class RenderWidgetHost;
+class SkBitmap;
+
+// This class MUST be destroyed after the RenderWidgetHosts, since it installs
+// a painting observer that is not removed.
+class ThumbnailGenerator : public RenderWidgetHostPaintingObserver,
+                           public NotificationObserver {
+ public:
+  ThumbnailGenerator();
+  ~ThumbnailGenerator();
+
+  SkBitmap GetThumbnailForRenderer(RenderWidgetHost* renderer) const;
+
+#ifdef UNIT_TEST
+  // When true, the class will not use a timeout to do the expiration. This
+  // will cause expiration to happen on the next run of the message loop.
+  // Unit tests case use this to test expiration by choosing when the message
+  // loop runs.
+  void set_no_timeout(bool no_timeout) { no_timeout_ = no_timeout; }
+#endif
+
+ private:
+  // RenderWidgetHostPaintingObserver implementation.
+  virtual void WidgetWillDestroyBackingStore(RenderWidgetHost* widget,
+                                             BackingStore* backing_store);
+  virtual void WidgetDidUpdateBackingStore(RenderWidgetHost* widget);
+
+  // NotificationObserver interface.
+  virtual void Observe(NotificationType type,
+                       const NotificationSource& source,
+                       const NotificationDetails& details);
+
+  // Indicates that the given widget has changed is visibility.
+  void WidgetShown(RenderWidgetHost* widget);
+  void WidgetHidden(RenderWidgetHost* widget);
+
+  // Called when the given widget is destroyed.
+  void WidgetDestroyed(RenderWidgetHost* widget);
+
+  // Timer function called on a delay after a tab has been shown. It will
+  // invalidate the thumbnail for hosts with expired thumbnails in shown_hosts_.
+  void ShownDelayHandler();
+
+  // Removes the given host from the shown_hosts_ list, if it is there.
+  void EraseHostFromShownList(RenderWidgetHost* host);
+
+  NotificationRegistrar registrar_;
+
+  base::OneShotTimer<ThumbnailGenerator> timer_;
+
+  // A list of all RWHs that have been shown and need to have their thumbnail
+  // expired at some time in the future with the "slop" time has elapsed. This
+  // list will normally have 0 or 1 items in it.
+  std::vector<RenderWidgetHost*> shown_hosts_;
+
+  // See the setter above.
+  bool no_timeout_;
+
+  DISALLOW_COPY_AND_ASSIGN(ThumbnailGenerator);
+};
+
+#endif  // CHROME_BROWSER_TAB_CONTENTS_THUMBNAIL_GENERATOR_H_