Skip TransformCanvas calls for FunctorDrawables

Fix issue where attempts to render overscroll content
into the alpha 8 mask would crash if there are WebView
related Functors in the scene.

Provide implementations for getTypeName in SkDrawable instances
of FunctorDrawable.

Fixes: 203960959
Test: manual
Change-Id: Idf321d9bfcbe2b8ba1eb205eadcec95e55865305