Extract gpu line dashing to GrDashLinePathRenderer

Move line dashing logic from GrContext::drawPath to
GrDashLinePathRenderer. This makes it possible to let path renderers render arbitrary dashed paths.

End goal is to implement dashing in GrStencilAndCoverPathRenderer.

Review URL: https://codereview.chromium.org/1100073003
diff --git a/src/gpu/GrPathRendererChain.cpp b/src/gpu/GrPathRendererChain.cpp
index d11763b..915bdd2 100644
--- a/src/gpu/GrPathRendererChain.cpp
+++ b/src/gpu/GrPathRendererChain.cpp
@@ -35,7 +35,7 @@
                                                      const GrPipelineBuilder* pipelineBuilder,
                                                      const SkMatrix& viewMatrix,
                                                      const SkPath& path,
-                                                     const SkStrokeRec& stroke,
+                                                     const GrStrokeInfo& stroke,
                                                      DrawType drawType,
                                                      StencilSupport* stencilSupport) {
     if (!fInit) {