Get the viewing plane .. correctly

As I've mentioned in previous post, we can use window.innerHeight to get the current viewing plane for the browser. However, since there are 2 documents inside a browser, putting them in either of them gave different values.

- reason:
- window.innerHeight called in Chrome level, return the browser's height
- window.innerHeight called in document level, return the viewpoint's height

- fixed using document.defaultView

This is a diagram taken from MDC:

#document
  window                 main-window
     ...
     browser
         #document
              window         myExtensionWindow)

As you can see, since they are on different levels, calling window.innerHeight will gave different values. The higher <window> is the window for the whole browser, whereas the lower <window> is the window of the viewing plane.