Improve caching of dashed paths in GrStencilAndCoverPathRenderer

Improve caching of dashed paths in GrStencilAndCoverPathRenderer

Improve caching of dashed paths in GrStencilAndCoverPathRenderer.
Look up the (NVPR specific) GrGLPath based on GrStrokeInfo and
the original path.

Use unique keys for all GrPaths.

Dash the path with Skia dash stroker and use that path geometry for
NVPR path.

NVPR internal dashing stroke is not used, because the dashing
implementation of NVPR does not match Skia implementation.

Review URL: https://codereview.chromium.org/1116123003