pull out clip code that will be shared

This clip code will be shared with direct-to-op text drawing
path.

Change-Id: I6744a93cb75b555e91b3b016d5604d3ba81b02fe
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/355977
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
Commit-Queue: Herb Derby <herb@google.com>
1 file changed