In Chromium these functions are only called from the Mac unit tests.
They are overrides of a deprecated function on SkBaseDevice.

*However*, that deprecated function is still called by SkCanvas::DeviceCM::updateMC().

Since they cache transforms and clips that we need to plumb through to native canvases (HDC on Windows, cairo_t on Cairo, CGContext on Mac) we may need some way to replace them in the SkRasterCanvasLayerAllocator future; intercepting draws to native-backed layers? Is that another argument for subclassing instead of strategizing?

Note also that SkDevice.h says overrides of setMatrixClip() *must* call the base class implementation, but the Chrome overrides do not do so.