Adding split view divider widget.

athena/common/drag_handle.h

Index: athena/common/drag_handle.h
diff --git a/athena/common/drag_handle.h b/athena/common/drag_handle.h
new file mode 100644
index 0000000000000000000000000000000000000000..bc32133630ec7017e3e32c5835adab93b7b1535e
--- /dev/null
+++ b/athena/common/drag_handle.h
@@ -0,0 +1,61 @@
+// 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_COMMON_DRAG_HANDLE_H_
+#define ATHENA_COMMON_DRAG_HANDLE_H_
+
+#include "athena/athena_export.h"
+
+namespace views {
+class View;
+}
+
+namespace athena {
+// DragHandle will notify it's delegate of the scroll gestures it receives
+// through the ScrollDelegate interface.
+class DragHandle {
+ public:
+  class ScrollDelegate {
+   public:
+    virtual ~ScrollDelegate() {}
+
+    // 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;

[sadrul, 2014/09/12 04:30:36]

Maybe HandleScrollBegin() could return a bool indicating whether the delegate is
going to handle the drag gesture or not.

[mfomitchev, 2014/09/12 20:49:07]

Yeah.. if we are not going to unify DragHandle::ScrollDelegate with
BezelController::ScrollDelegate, it might be worth it. Although it might come in
handy in the future (e.g. for using a different highlight color when
HandleCanScroll() is false). Also being able to short-circuit in
DragHandle::OnGestureEvent is kind of nice... 

+  };
+
+  virtual ~DragHandle();
+
+  enum ScrollDirection { VERTICAL, HORIZONTAL };
+};
+
+// The handle view occupies the entire space given to it, showing a rectangular
+// handle in the center of the view on a black background. Preferred width and
+// height define the preferred visual extents of the rectangular handle.
+// |margin| defines the minimum margins between the visual handle and the
+// borders of the entire handle view.
+ATHENA_EXPORT views::View* CreateDragHandleView(
+    DragHandle::ScrollDirection scroll_direction,
+    DragHandle::ScrollDelegate* delegate,
+    int preferred_width,
+    int preferred_height,
+    int margin);
+
+}  // namespace athena
+
+#endif  // ATHENA_COMMON_DRAG_HANDLE_H_