Added toString to SkMaskFilter-derived classes

Added toString to SkMaskFilter-derived classes

[DerekS, 2013-03-18 17:11:07]

the idea looks OK to me, but want to get mike's opinion as it is a pretty
pervasive change.

[reed1, 2013-03-18 17:25:39]

Is there a useful unittest for this? (not sure)
Can you add a dump of the results to the CL (so we can at least see that the
toString functions returned something useful-looking)?

[robertphillips, 2013-03-18 17:50:20]

These methods are used by the debugger to display the paint details for a
command. I test them out by dumping the GMs to skps and looking for examples in
the captured and GM skps. Here are some samples:

------------------------
desk_youtube.skp:

MaskFilter:
	SkBlurMaskFilterImpl: (radius: 1 style: normal flags: (HighQuality))

------------------------
GM:drawbitmapmatrix:

MaskFilter:
	SkBlurMaskFilterImpl: (radius: 5 style: normal flags:
(IgnoreXform|HighQuality))

------------------------
GM:samplerstress:

MaskFilter:
	SkStippleMaskFilter: ()

------------------------
GM:texteffects:

MaskFilter:
	SkEmbossMaskFilter: (direction: (0.57735026, 0.57735026, 0.57735026) ambient:
64 specular: 64 blurRadius: 3)

Note that the table, kernel33, dark and reduceNoise mask filters don't appear in
either the captured skps or the gms.

[reed1, 2013-03-18 17:51:17]

lgtm

[robertphillips, 2013-03-18 17:54:02]

committed as r8194