define SK_LATE_DITHER to guard moving it

This guards https://skia-review.googlesource.com/c/skia/+/291876
for Blink rebaselines.

Bug: skia:10000
Change-Id: I42b2318dff80c38de51ab0c87ed91266401171d3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2216350
Commit-Queue: Mike Klein <mtklein@google.com>
Commit-Queue: Mike Reed <reed@google.com>
Auto-Submit: Mike Klein <mtklein@google.com>
Reviewed-by: Mike Reed <reed@google.com>
Cr-Commit-Position: refs/heads/master@{#771871}

skia/config/SkUserConfig.h

@@ -221,6 +221,8 @@ SK_API void SkDebugf_FileLine(const char* file,
 #define SK_SUPPORT_LEGACY_MATRIX_FACTORIES
 #endif
 
+#define SK_LATE_DITHER
+
 ///////////////////////// Imported from BUILD.gn and skia_common.gypi
 
 /* In some places Skia can use static initializers for global initialization,