add flag to stage removing drawloopers

Bug: skia:4783
Change-Id: I02c4388dd5c998d132a089caf7f6244c46030d00
Reviewed-on: https://chromium-review.googlesource.com/c/1456978
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@{#629733}

skia/config/SkUserConfig.h

@@ -144,6 +144,11 @@ SK_API void SkDebugf_FileLine(const char* file, int line, bool fatal,
 #define SK_USE_LEGACY_DISTANCE_FIELDS
 #endif
 
+// skbug.com/4783
+#ifndef SK_SUPPORT_LEGACY_DRAWLOOPER
+#define SK_SUPPORT_LEGACY_DRAWLOOPER
+#endif
+
 // Skia is enabling this feature soon. Chrome probably does
 // not want it for M64
 #ifndef SK_DISABLE_EXPLICIT_GPU_RESOURCE_ALLOCATION