Revert of Remove SK_SUPPORT_LEGACY_DEEPFLATTENING.

src/effects/SkColorFilters.cpp

Index: src/effects/SkColorFilters.cpp
diff --git a/src/effects/SkColorFilters.cpp b/src/effects/SkColorFilters.cpp
index 92e6f432f17c24cf5c2d2b020ccc769b88ddeb8d..e085281aa5e3901741f6d4c7287da6136749a029 100644
--- a/src/effects/SkColorFilters.cpp
+++ b/src/effects/SkColorFilters.cpp
@@ -83,6 +83,17 @@
         buffer.writeColor(fColor);
         buffer.writeUInt(fMode);
     }
+
+#ifdef SK_SUPPORT_LEGACY_DEEPFLATTENING
+    SkModeColorFilter(SkReadBuffer& buffer) {
+        fColor = buffer.readColor();
+        fMode = (SkXfermode::Mode)buffer.readUInt();
+        if (buffer.isValid()) {
+            this->updateCache();
+            buffer.validate(SkIsValidMode(fMode));
+        }
+    }
+#endif
 
 private:
     SkColor             fColor;