Add flag to stage filtering change for pictureshaders

This may allow us to separate two issues: moving away from (deprecated)
SkFilterquality, and exactly how to post-sampling picture-shaders.

Change-Id: Icb81d5779173a518ecc4bee1fcfcbf3223337ee0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2626169
Commit-Queue: Mike Reed <reed@google.com>
Commit-Queue: Florin Malita <fmalita@chromium.org>
Reviewed-by: Florin Malita <fmalita@chromium.org>
Cr-Commit-Position: refs/heads/master@{#842823}

skia/config/SkUserConfig.h

@@ -221,6 +221,12 @@ SK_API void SkDebugf_FileLine(const char* file,
 // Max. verb count for paths rendered by the edge-AA tessellating path renderer.
 #define GR_AA_TESSELLATOR_MAX_VERB_COUNT 100
 
+
+#ifndef SK_SUPPORT_NEAREST_PICTURESHADER_POSTFILTER
+#define SK_SUPPORT_NEAREST_PICTURESHADER_POSTFILTER
+#endif
+
+
 #ifndef SK_SUPPORT_LEGACY_AAA_CHOICE
 #define SK_SUPPORT_LEGACY_AAA_CHOICE
 #endif