Adding split view divider widget.

athena/util/drag_handle.h

+// 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 {
+// DragHandle will notify it's delegate of the scroll gestures it receives
+// through the ScrollDelegate interface.
+class DragHandle {

[pkotwicz, 2014/09/16 20:02:47]

Nuke the DragHandle class. No one instantiates it. Maybe rename
DragHandle::ScrollDelegate to DragHandleScrollDelegate

[mfomitchev, 2014/09/22 21:10:59]

Done.

+ 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;

[pkotwicz, 2014/09/16 20:02:47]

I wonder whether this is overkill. In the bezel case, we just ignore
ScrollBegin(), ScrollUpdate(), ScrollEnd() if scrolling is not allowed

[mfomitchev, 2014/09/22 21:10:59]

Actually we don't ignore update/end once we receive a begin. Start the
drag-from-the-bezel, then rotate the device - you can still continue dragging.
We don't mark the events as handled in this case though, which I think is a bug,
I created crbug.com/416564 for this.

[pkotwicz, 2014/09/23 05:13:39]

Just to double check, we are planning on having HandleCanScroll() eventually
sometimes return false? If we are, then I am ok with having this method.

I can't think of a case where we would want HandleCanScroll() to be false. We
want to prevent multiple gestures from occurring simultaneously.
http://crbug.com/416725 (e.g. title drag and bezel drag) but I think we will end
up preventing this in some other way.

[mfomitchev, 2014/09/23 15:46:02]

Yes, good point. I added it because I thought we were going to unify
DragHandleScrollDelegate with BezelController::ScrollDelegate, but it doesn't
look like that's going to happen. Done.

+  };
+
+  virtual ~DragHandle();
+
+  enum ScrollDirection { VERTICAL, HORIZONTAL };
+};
+
+// Creates a handle view which notifies the delegate of the scrolls performed on
+// it.
+ATHENA_EXPORT views::View* CreateDragHandleView(
+    DragHandle::ScrollDirection scroll_direction,
+    DragHandle::ScrollDelegate* delegate,
+    int preferred_width,
+    int preferred_height);
+
+}  // namespace athena
+
+#endif  // ATHENA_UTIL_DRAG_HANDLE_H_