add flag to stage api change to SkShader tilemodes

Bug: skia:8937
Change-Id: If9bb3f06d4fad64e2e44d4cae96aa2a0db0a04c1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1551119
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@{#647328}

skia/config/SkUserConfig.h

@@ -169,6 +169,10 @@ SK_API void SkDebugf_FileLine(const char* file, int line, bool fatal,
 #define SK_ENABLE_LEGACY_TEXT_COLOR
 #endif
 
+#ifndef SK_SUPPORT_LEGACY_TILEMODE_ENUM
+#define SK_SUPPORT_LEGACY_TILEMODE_ENUM
+#endif
+
 // We're turning this off indefinitely,
 // until we can figure out some fundamental problems with its approach.
 //