Remove all calls to SkCanvas::getClipStack from HWUI unit tests

Refactor HWUI unit tests to not invoke SkCanvas::getClipStack,
because this Skia API is going to be deprecated.

Test: Build and ran sailfish-eng. Ran HWUI unit tests.
Change-Id: Iac277aa26fbe9e2a0860cde2dd43732ed1c4c4e3
3 files changed