Use stencil ops that don't issue writes whenever possible

src/gpu/GrStencilAndCoverPathRenderer.cpp

Index: src/gpu/GrStencilAndCoverPathRenderer.cpp
diff --git a/src/gpu/GrStencilAndCoverPathRenderer.cpp b/src/gpu/GrStencilAndCoverPathRenderer.cpp
index f871c3da7328b23b163ea8fda8231f9bb38b7f7e..6cd982c515bef2642d9a77db9c93681dacce9f61 100644
--- a/src/gpu/GrStencilAndCoverPathRenderer.cpp
+++ b/src/gpu/GrStencilAndCoverPathRenderer.cpp
@@ -102,7 +102,7 @@ bool GrStencilAndCoverPathRenderer::onDrawPath(const DrawPathArgs& args) {
 
     if (path.isInverseFillType()) {
         GR_STATIC_CONST_SAME_STENCIL(kInvertedStencilPass,
-            kZero_StencilOp,
+            kKeep_StencilOp,
             kZero_StencilOp,
             // We know our rect will hit pixels outside the clip and the user bits will be 0
             // outside the clip. So we can't just fill where the user bits are 0. We also need to
@@ -141,7 +141,7 @@ bool GrStencilAndCoverPathRenderer::onDrawPath(const DrawPathArgs& args) {
     } else {
         GR_STATIC_CONST_SAME_STENCIL(kStencilPass,
             kZero_StencilOp,
-            kZero_StencilOp,
+            kKeep_StencilOp,
             kNotEqual_StencilFunc,
             0xffff,
             0x0000,