Make onPrepareDraws const

src/gpu/GrPathUtils.h

Index: src/gpu/GrPathUtils.h
diff --git a/src/gpu/GrPathUtils.h b/src/gpu/GrPathUtils.h
index 385cc0e47097585da4230a1678ee455f2869b006..4874fa2aef08bda026b0c557dc170a14ce9e5c89 100644
--- a/src/gpu/GrPathUtils.h
+++ b/src/gpu/GrPathUtils.h
@@ -74,7 +74,7 @@ namespace GrPathUtils {
          * vertices is a pointer to the first vertex.
          */
         template <int N, size_t STRIDE, size_t UV_OFFSET>
-        void apply(const void* vertices) {
+        void apply(const void* vertices) const {
             intptr_t xyPtr = reinterpret_cast<intptr_t>(vertices);
             intptr_t uvPtr = reinterpret_cast<intptr_t>(vertices) + UV_OFFSET;
             float sx = fM[0];