Simplify flattening to just write enough to call the factory

src/effects/SkDisplacementMapEffect.cpp

Index: src/effects/SkDisplacementMapEffect.cpp
diff --git a/src/effects/SkDisplacementMapEffect.cpp b/src/effects/SkDisplacementMapEffect.cpp
index bae7ac098c7bdf376754ff508af432e3a3de45b6..eb479c0f22137a8c7691396250c2b504317aa479 100644
--- a/src/effects/SkDisplacementMapEffect.cpp
+++ b/src/effects/SkDisplacementMapEffect.cpp
@@ -174,6 +174,7 @@ SkDisplacementMapEffect::SkDisplacementMapEffect(ChannelSelectorType xChannelSel
 SkDisplacementMapEffect::~SkDisplacementMapEffect() {
 }
 
+#ifdef SK_SUPPORT_LEGACY_DEEPFLATTENING
 SkDisplacementMapEffect::SkDisplacementMapEffect(SkReadBuffer& buffer)
   : INHERITED(2, buffer)
 {
@@ -184,6 +185,15 @@ SkDisplacementMapEffect::SkDisplacementMapEffect(SkReadBuffer& buffer)
                     channel_selector_type_is_valid(fYChannelSelector) &&
                     SkScalarIsFinite(fScale));
 }
+#endif
+
+SkFlattenable* SkDisplacementMapEffect::CreateProc(SkReadBuffer& buffer) {
+    SK_IMAGEFILTER_UNFLATTEN_COMMON(2);
+    ChannelSelectorType xsel = (ChannelSelectorType)buffer.readInt();
+    ChannelSelectorType ysel = (ChannelSelectorType)buffer.readInt();
+    SkScalar scale = buffer.readScalar();
+    return Create(xsel, ysel, scale, common.inputAt(0), common.inputAt(1), &common.cropRect());
+}
 
 void SkDisplacementMapEffect::flatten(SkWriteBuffer& buffer) const {
     this->INHERITED::flatten(buffer);