Added new arguments for screenshot request

Added frameScaleX and frameScaleY to replace frameScale to allow callers
to specify an X and Y scale separately.

Added grayscale flag to allow the caller to take the screenshot
in grayscale.

Test: Screenshot in grayscale
Bug: 155825630
Change-Id: I00521c2fbc1a847586bde9c23beafa343115d4f5