New implementation of handling didUpdateReactSubviews and didUpdateReactSubviews events

Summary:
Motivation:
* Current implementation of `didUpdateReactSubviews` relies on `processUpdatedProperties:parentProperties:` method of RCTShadowView, which we plan to remove.
* The existing implementation does not call handlers on unmounted nodes (because they are not part of traversing tree), which is not correct.
* The current implementation is tight with RCTComponentData, which is conceptually wrong, it should be a UIManager thing.
* The new implementation must be much more performant because of simplicity. (We can measure it only after removing `processUpdatedProperties`.)

Reviewed By: mmmulani

Differential Revision: D6595780

fbshipit-source-id: a517207c17b5d5db839c9ce99a37136292acf78c

React/Views/RCTComponent.h

@@ -36,8 +36,6 @@ typedef void (^RCTBubblingEventBlock)(NSDictionary *body);
 // View/ShadowView is a root view
 - (BOOL)isReactRootView;
 
-@optional
-
 /**
  * Called each time props have been set.
  * Not all props have to be set - React can set only changed ones.

React/Views/RCTComponentData.m

@@ -355,10 +355,6 @@ static RCTPropBlock createNSInvocationSetter(NSMethodSignature *typeSignature, S
   [props enumerateKeysAndObjectsUsingBlock:^(NSString *key, id json, __unused BOOL *stop) {
     [self propBlockForKey:key isShadowView:NO](view, json);
   }];
-
-  if ([view respondsToSelector:@selector(didSetProps:)]) {
-    [view didSetProps:[props allKeys]];
-  }
 }
 
 - (void)setProps:(NSDictionary<NSString *, id> *)props forShadowView:(RCTShadowView *)shadowView
@@ -370,10 +366,6 @@ static RCTPropBlock createNSInvocationSetter(NSMethodSignature *typeSignature, S
   [props enumerateKeysAndObjectsUsingBlock:^(NSString *key, id json, __unused BOOL *stop) {
     [self propBlockForKey:key isShadowView:YES](shadowView, json);
   }];
-
-  if ([shadowView respondsToSelector:@selector(didSetProps:)]) {
-    [shadowView didSetProps:[props allKeys]];
-  }
 }
 
 - (NSDictionary<NSString *, id> *)viewConfig

React/Views/RCTShadowView.m

@@ -41,7 +41,6 @@ typedef NS_ENUM(unsigned int, meta_prop_t) {
   BOOL _recomputePadding;
   BOOL _recomputeMargin;
   BOOL _recomputeBorder;
-  BOOL _didUpdateSubviews;
   YGValue _paddingMetaProps[META_PROP_COUNT];
   YGValue _marginMetaProps[META_PROP_COUNT];
   YGValue _borderMetaProps[META_PROP_COUNT];
@@ -263,19 +262,6 @@ static void RCTProcessMetaPropsBorder(const YGValue metaProps[META_PROP_COUNT],
 - (NSDictionary<NSString *, id> *)processUpdatedProperties:(NSMutableSet<RCTApplierBlock> *)applierBlocks
                                           parentProperties:(NSDictionary<NSString *, id> *)parentProperties
 {
-  // TODO: we always refresh all propagated properties when propagation is
-  // dirtied, but really we should track which properties have changed and
-  // only update those.
-
-  if (_didUpdateSubviews) {
-    _didUpdateSubviews = NO;
-    [self didUpdateReactSubviews];
-    [applierBlocks addObject:^(NSDictionary<NSNumber *, UIView *> *viewRegistry) {
-      UIView *view = viewRegistry[self->_reactTag];
-      [view didUpdateReactSubviews];
-    }];
-  }
-
   return parentProperties;
 }
 
@@ -435,7 +421,6 @@ static void RCTProcessMetaPropsBorder(const YGValue metaProps[META_PROP_COUNT],
     YGNodeInsertChild(_yogaNode, subview.yogaNode, (uint32_t)atIndex);
   }
   subview->_superview = self;
-  _didUpdateSubviews = YES;
   [self dirtyText];
   [self dirtyPropagation];
 }
@@ -444,7 +429,6 @@ static void RCTProcessMetaPropsBorder(const YGValue metaProps[META_PROP_COUNT],
 {
   [subview dirtyText];
   [subview dirtyPropagation];
-  _didUpdateSubviews = YES;
   subview->_superview = nil;
   [_reactSubviews removeObject:subview];
   if (![self isYogaLeafNode]) {

React/Views/UIView+React.h

@@ -60,6 +60,12 @@
  */
 - (void)didUpdateReactSubviews;
 
+/**
+ * Called each time props have been set.
+ * The default implementation does nothing.
+ */
+- (void)didSetProps:(NSArray<NSString *> *)changedProps;
+
 /**
  * Used by the UIIManager to set the view frame.
  * May be overriden to disable animation, etc.

React/Views/UIView+React.m

@@ -172,6 +172,11 @@
   }
 }
 
+- (void)didSetProps:(__unused NSArray<NSString *> *)changedProps
+{
+  // The default implementation does nothing.
+}
+
 - (void)reactSetFrame:(CGRect)frame
 {
   // These frames are in terms of anchorPoint = topLeft, but internally the