Disable deprecated Skia xfermodes

This is a companion to https://codereview.chromium.org/1645633003/ (Hide SkPixelXorXfermode from Chrome)

Review URL: https://codereview.chromium.org/1644703002

Cr-Commit-Position: refs/heads/master@{#371905}

skia/config/SkUserConfig.h

@@ -245,6 +245,10 @@ SK_API void SkDebugf_FileLine(const char* file, int line, bool fatal,
  */
 #define SK_ALLOW_STATIC_GLOBAL_INITIALIZERS 0
 
+/* Don't include the xfermodes deprecated in Skia
+ */
+#define SK_INCLUDE_DEPRECATED_XFERMODES 0
+
 /* This flag forces Skia not to use typographic metrics with GDI.
  */
 #define SK_GDI_ALWAYS_USE_TEXTMETRICS_FOR_FONT_METRICS