add SK_SUPPORT_LEGACY_IMAGEFILTER_TO_COLORFILTER to guard skia change

in support of https://codereview.chromium.org/986353002/

BUG=

Review URL: https://codereview.chromium.org/1115713003

Cr-Commit-Position: refs/heads/master@{#327537}

skia/config/SkUserConfig.h

@@ -257,6 +257,10 @@ SK_API void SkDebugf_FileLine(const char* file, int line, bool fatal,
 #   define SK_SUPPORT_LEGACY_PUBLIC_IMAGEINFO_FIELDS
 #endif
 
+#ifndef    SK_SUPPORT_LEGACY_IMAGEFILTER_TO_COLORFILTER
+#   define SK_SUPPORT_LEGACY_IMAGEFILTER_TO_COLORFILTER
+#endif
+
 #ifndef    SK_IGNORE_ETC1_SUPPORT
 #   define SK_IGNORE_ETC1_SUPPORT
 #endif