Adding a Views scrollbar implementation.

views/controls/scrollbar/base_scroll_bar_thumb.h

Index: views/controls/scrollbar/base_scroll_bar_thumb.h
diff --git a/views/controls/scrollbar/base_scroll_bar_thumb.h b/views/controls/scrollbar/base_scroll_bar_thumb.h
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+++ b/views/controls/scrollbar/base_scroll_bar_thumb.h
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+// Copyright (c) 2011 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 VIEWS_CONTROLS_SCROLLBAR_BASE_SCROLL_BAR_THUMB_H_
+#define VIEWS_CONTROLS_SCROLLBAR_BASE_SCROLL_BAR_THUMB_H_
+#pragma once
+
+#include "ui/gfx/size.h"
+#include "views/controls/button/custom_button.h"
+#include "views/controls/scrollbar/scroll_bar.h"
+#include "views/view.h"
+
+namespace gfx {
+class Canvas;
+}
+
+namespace views {
+
+class BaseScrollBar;
+
+///////////////////////////////////////////////////////////////////////////////
+//
+// BaseScrollBarThumb
+//
+//  A view that acts as the thumb in the scroll bar track that the user can
+//  drag to scroll the associated contents view within the viewport.
+//
+///////////////////////////////////////////////////////////////////////////////
+class VIEWS_EXPORT BaseScrollBarThumb : public View {
+ public:
+  explicit BaseScrollBarThumb(BaseScrollBar* scroll_bar);
+  virtual ~BaseScrollBarThumb();
+
+  // Sets the size (width or height) of the thumb to the specified value.
+  void SetSize(int size);
+
+  // Retrieves the size (width or height) of the thumb.
+  int GetSize() const;
+
+  // Sets the position of the thumb on the x or y axis.
+  void SetPosition(int position);
+
+  // Gets the position of the thumb on the x or y axis.
+  int GetPosition() const;
+
+  // View overrides:
+  virtual gfx::Size GetPreferredSize() OVERRIDE = 0;
+
+ protected:
+  // View overrides:
+  virtual void OnPaint(gfx::Canvas* canvas) OVERRIDE = 0;
+  virtual void OnMouseEntered(const MouseEvent& event) OVERRIDE;
+  virtual void OnMouseExited(const MouseEvent& event) OVERRIDE;
+  virtual bool OnMousePressed(const MouseEvent& event) OVERRIDE;
+  virtual bool OnMouseDragged(const MouseEvent& event) OVERRIDE;
+  virtual void OnMouseReleased(const MouseEvent& event) OVERRIDE;
+  virtual void OnMouseCaptureLost() OVERRIDE;
+
+  CustomButton::ButtonState GetState() const;
+  // Update our state and schedule a repaint when the mouse moves over us.
+  void SetState(CustomButton::ButtonState state);
+
+ private:
+  // The BaseScrollBar that owns us.
+  BaseScrollBar* scroll_bar_;
+
+  int drag_start_position_;
+
+  // The position of the mouse on the scroll axis relative to the top of this
+  // View when the drag started.
+  int mouse_offset_;
+
+  // The current state of the thumb button.
+  CustomButton::ButtonState state_;
+
+  DISALLOW_COPY_AND_ASSIGN(BaseScrollBarThumb);
+};
+
+}  // namespace views
+
+#endif  // VIEWS_CONTROLS_SCROLLBAR_BASE_SCROLL_BAR_THUMB_H_