Avoid reentrance on ClipArea APIs

bug:28144676

Calling ClipArea::clipRegion from within ClipArea::clipPathWithTransform
has us handling op-based special casing twice, which caused all clip
paths to appear to be replace ops.

Change-Id: Ib842db53ffed4eee29470f773d59a3a1d07a1a0e
2 files changed