Add GrContextOptions flag to disable distance field path renderer.

src/gpu/GrPathRendererChain.h

Index: src/gpu/GrPathRendererChain.h
diff --git a/src/gpu/GrPathRendererChain.h b/src/gpu/GrPathRendererChain.h
index ade30551ae5011a014e1229767a1d87a916ccb75..2a11a19cda86f7ac7fd519bbbc492c8371a060b2 100644
--- a/src/gpu/GrPathRendererChain.h
+++ b/src/gpu/GrPathRendererChain.h
@@ -23,7 +23,10 @@ class GrContext;
  */
 class GrPathRendererChain : public SkNoncopyable {
 public:
-    GrPathRendererChain(GrContext* context);
+    struct Options {
+        bool fDisableDistanceFieldRenderer = false;
+    };
+    GrPathRendererChain(GrContext* context, const Options&);
 
     ~GrPathRendererChain();