Fix default width and height for PopupWindow's decor view

Fixes a regression whereby failing to explicitly set a width and height
would cause the popup window's decor view to be 0 width and height.

Also deprecates unnecessary method for setting window width and
height spec and replaces with less-confusing setters.

Cleans up javadoc for modified methods.

Bug: 19538371
Change-Id: I20da3ff02ad12e99adf14c056edd1a890b5c322a