This change also modifies 9-patch drawables to fix the following
issues.  In order to draw key background drawable just on the
coordinates we want, we have to know where an actual "visible" part is
in the drawable.  The only clue we can use is "padding" of the
drawable.  To achieve this, the 9-patch drawable must have its
"visible" part marked as "content".  Please refer the Bug: 4948171 for
more detailed explanation.

This change also reverts the following "black" drawables back from
Gingerbread because recent change broke these (I70019a91).
  * drawable-hdpi/sym_bkeyboard_*.png
  * drawable-hdpi/btn_keyboard_key_*_stone.9.png

Bug: 4948171
Change-Id: I6e4d03b3144caa95c793aac97af22df34c5f454f