Use GrVertexWriter in GrSmallPathRenderer

Make TriStrip a templated rect, with a helper for SkRect.
Added writeQuadValue overload for GrQuad.

Bug: skia:
Change-Id: I2934e5dbb086c5dbe0cc4846176bab8ccc324cf6
Reviewed-on: https://skia-review.googlesource.com/c/171534
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
diff --git a/src/gpu/ops/GrRegionOp.cpp b/src/gpu/ops/GrRegionOp.cpp
index d824609..7f1ad81 100644
--- a/src/gpu/ops/GrRegionOp.cpp
+++ b/src/gpu/ops/GrRegionOp.cpp
@@ -121,7 +121,7 @@
             SkRegion::Iterator iter(fRegions[i].fRegion);
             while (!iter.done()) {
                 SkRect rect = SkRect::Make(iter.rect());
-                vertices.writeQuad(GrVertexWriter::TriStrip{ rect }, color);
+                vertices.writeQuad(GrVertexWriter::TriStripFromRect(rect), color);
                 iter.next();
             }
         }