add flag to migrate away from SkMScalar

See Skia CLs https://skia-review.googlesource.com/c/skia/+/265298
             https://skia-review.googlesource.com/c/skia/+/265299

Change-Id: I159f471befddee2877cb631c461e075b2793ef44
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2011044
Commit-Queue: Mike Reed <reed@google.com>
Reviewed-by: Florin Malita <fmalita@chromium.org>
Cr-Commit-Position: refs/heads/master@{#733504}

skia/config/SkUserConfig.h

@@ -226,6 +226,14 @@ SK_API void SkDebugf_FileLine(const char* file,
 #define SK_SUPPORT_LEGACY_AAA_CHOICE
 #endif
 
+#ifndef SK_SUPPORT_LEGACY_MSCALAR
+#define SK_SUPPORT_LEGACY_MSCALAR
+#endif
+
+#ifndef SK_SUPPORT_LEGACY_COLORSPACE_INCLUDES_MATRIX44
+#define SK_SUPPORT_LEGACY_COLORSPACE_INCLUDES_MATRIX44
+#endif
+
 // We're turning this off indefinitely,
 // until we can figure out some fundamental problems with its approach.
 //