Add Skia build flag for upcoming sweep gradient change

skia/config/SkUserConfig.h

 /*
  * Copyright (C) 2006 The Android Open Source Project
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *      http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
@@ skipping 202 matching lines @@
 // Remove this after we fixed all the issues related to the new SDF algorithm
 // (https://codereview.chromium.org/1643143002)
 #ifndef    SK_USE_LEGACY_DISTANCE_FIELDS
 #   define SK_USE_LEGACY_DISTANCE_FIELDS
 #endif
 
 #ifndef SK_DISABLE_DEFERRED_PROXIES
 #define SK_DISABLE_DEFERRED_PROXIES
 #endif
 
+#ifndef SK_LEGACY_SWEEP_GRADIENT
+#define SK_LEGACY_SWEEP_GRADIENT
+#endif
+
 ///////////////////////// Imported from BUILD.gn and skia_common.gypi
 
 /* In some places Skia can use static initializers for global initialization,
  *  or fall back to lazy runtime initialization. Chrome always wants the latter.
  */
 #define SK_ALLOW_STATIC_GLOBAL_INITIALIZERS 0
 
 /* This flag forces Skia not to use typographic metrics with GDI.
  */
 #define SK_GDI_ALWAYS_USE_TEXTMETRICS_FOR_FONT_METRICS
@@ skipping 10 matching lines @@
 #define GR_GL_CUSTOM_SETUP_HEADER   "GrGLConfig_chrome.h"
 
 // mtklein's fiddling with Src / SrcOver.  Will rebaseline these only once when done.
 #define SK_SUPPORT_LEGACY_X86_BLITS
 
 #define SK_DISABLE_TILE_IMAGE_FILTER_OPTIMIZATION
 
 // ===== End Chrome-specific definitions =====
 
 #endif