Fabric: Props now have a revision number

Summary:
Props now have a special value that represents generation number of `Props` object, which
increases when the object was constructed with some source `Props` object.

Reviewed By: mdvacca

Differential Revision: D14293939

fbshipit-source-id: 4782bf33ccf37623d4079c09cc4d0268bb6c2690

ReactCommon/fabric/core/shadownode/Props.cpp

@@ -14,7 +14,8 @@ namespace facebook {
 namespace react {
 
 Props::Props(const Props &sourceProps, const RawProps &rawProps)
-    : nativeId(convertRawProp(rawProps, "nativeID", sourceProps.nativeId))
+    : nativeId(convertRawProp(rawProps, "nativeID", sourceProps.nativeId)),
+      revision(sourceProps.revision + 1)
 #ifdef ANDROID
       ,
       rawProps((folly::dynamic)rawProps)

ReactCommon/fabric/core/shadownode/Props.h

@@ -31,6 +31,15 @@ class Props : public virtual Sealable, public virtual DebugStringConvertible {
 
   const std::string nativeId;
 
+  /*
+   * Special value that represents generation number of `Props` object, which
+   * increases when the object was constructed with some source `Props` object.
+   * Default props objects (that was constructed using default constructor) have
+   * revision equals `0`.
+   * The value might be used for optimization purposes.
+   */
+  const int revision{0};
+
 #ifdef ANDROID
   const folly::dynamic rawProps = folly::dynamic::object();
 #endif