add guard for convexity changes in skia

See skia cl https://skia-review.googlesource.com/c/skia/+/173226

Change-Id: Id097cfd805140a297dff07bbfae1037f2a18467a
Reviewed-on: https://chromium-review.googlesource.com/c/1352679Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Mike Reed <reed@google.com>
Cr-Commit-Position: refs/heads/master@{#611865}

skia/config/SkUserConfig.h

@@ -150,6 +150,11 @@ SK_API void SkDebugf_FileLine(const char* file, int line, bool fatal,
 #define SK_USE_LEGACY_DISTANCE_FIELDS
 #endif
 
+// To stage layout result changes (minor) related to convexity calculations
+#ifndef SK_SUPPORT_LEGACY_CACHE_CONVEXITY
+#define SK_SUPPORT_LEGACY_CACHE_CONVEXITY
+#endif
+
 // Skia is enabling this feature soon. Chrome probably does
 // not want it for M64
 #ifndef SK_DISABLE_EXPLICIT_GPU_RESOURCE_ALLOCATION