Bug 1060090 part 1: Rename ParseBackgroundPositionValues to ParsePositionValue. r=heycam
Bug 1060090 part 2: Spin out "ComputePositionValue", and rename its helper "ComputeBackgroundPositionCoord" to "ComputePositionCoord". r=heycam
Bug 1060090 part 3: Refactor getComputedStyle implementation for 'background-position' to use helper-method for <position> & its sub-parts. r=heycam
Bug 1060090 part 4: Allow computed-style 'Position' struct to have different initial values beyond just 0% 0%. r=heycam
Bug 1060090 part 5: Refactor StyleAnimationValue <position>-handling code to use helper-methods. r=heycam