Breaking Change: dart:html Point & Rect

[Pete Blois]

FYI-

We're introducing Point and Rect types to dart:html and changing some APIs to use them.

Input events are having their position properties change from clientX & clientY to a single Point field. 

The old syntax is currently deprecated.

Old:

var x = mouseEvent.offsetX;

New:

var x = mouseEvent.offset.x;

Element.client* and Element.offset* properties have now become rects as well.

The old syntax is currently deprecated.

Old:

var top = Element.clientTop;

New:

var top = Element.client.top;

In addition, Element.getBoundingClientRect() now returns a Rect rather than a ClientRect. The ClientRect type has been hidden.