Adding split view divider widget.

athena/util/drag_handle.h

Index: athena/util/drag_handle.h
diff --git a/athena/util/drag_handle.h b/athena/util/drag_handle.h
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+++ b/athena/util/drag_handle.h
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+// Copyright 2014 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 ATHENA_UTIL_DRAG_HANDLE_H_
+#define ATHENA_UTIL_DRAG_HANDLE_H_
+
+#include "athena/athena_export.h"
+
+namespace views {
+class View;
+}
+
+namespace athena {
+class DragHandleScrollDelegate {
+ public:
+  virtual ~DragHandleScrollDelegate() {}
+
+  // Beginning of a scroll gesture.
+  virtual void HandleScrollBegin(float delta) = 0;
+
+  // End of the current scroll gesture.
+  virtual void HandleScrollEnd() = 0;
+
+  // Update of the scroll position for the currently active scroll gesture.
+  virtual void HandleScrollUpdate(float delta) = 0;
+
+  // Should return false if the delegate isn't going to react to the scroll
+  // events.
+  // As long as this returns false, the handle won't start scrolling. However
+  // if the scroll starts while HandleCanScroll() returns true and then the
+  // delegate's state changes mid-scrol and HandleCanScroll() starts to return
+  // false, the handle will continue scrolling and HandleScrollUpdate /
+  // HandleScrollEnd callbacks will be called on the delegate.
+  virtual bool HandleCanScroll() = 0;
+};
+
+enum DragHandleScrollDirection { DRAG_HANDLE_VERTICAL, DRAG_HANDLE_HORIZONTAL };
+
+// Creates a handle view which notifies the delegate of the scrolls performed on
+// it.
+ATHENA_EXPORT views::View* CreateDragHandleView(
+    DragHandleScrollDirection scroll_direction,
+    DragHandleScrollDelegate* delegate,
+    int preferred_width,
+    int preferred_height);
+
+}  // namespace athena
+
+#endif  // ATHENA_UTIL_DRAG_HANDLE_H_