add flag for skia assert change

BUG=
TBR=fmalita@chromium.org
NOTRY=True

Review URL: https://codereview.chromium.org/1144423003

Cr-Commit-Position: refs/heads/master@{#330936}

skia/config/SkUserConfig.h

@@ -265,6 +265,10 @@ SK_API void SkDebugf_FileLine(const char* file, int line, bool fatal,
 #   define SK_IGNORE_GPU_DITHER
 #endif
 
+#ifndef    SK_SUPPORT_LEGACY_UNBALANCED_PIXELREF_LOCKCOUNT
+#   define SK_SUPPORT_LEGACY_UNBALANCED_PIXELREF_LOCKCOUNT
+#endif
+
 #ifndef    SK_SUPPORT_LEGACY_INT_COLORMATRIX
 #   define SK_SUPPORT_LEGACY_INT_COLORMATRIX
 #endif