add SK_LEGACY_DRAWPICTURECALLBACK guard flag

Used until chrome switches to the new skia api

BUG=
TBR=robertphilips@chromium.org

Review URL: https://codereview.chromium.org/1014473005

Cr-Commit-Position: refs/heads/master@{#320830}

skia/config/SkUserConfig.h

@@ -245,6 +245,10 @@ SK_API void SkDebugf_FileLine(const char* file, int line, bool fatal,
 #   define SK_SUPPORT_LEGACY_GETTOPDEVICE
 #endif
 
+#ifndef    SK_LEGACY_DRAWPICTURECALLBACK
+#   define SK_LEGACY_DRAWPICTURECALLBACK
+#endif
+
 #ifndef    SK_SUPPORT_LEGACY_GETDEVICE
 #   define SK_SUPPORT_LEGACY_GETDEVICE
 #endif