Merge pull request #1231 from garrettmoon/reducePlaceholderFadeCost

[Placeholders] Only start a fading animation if we're visible. And a threadsafety fix.

AsyncDisplayKit/ASDisplayNode.mm

@@ -780,11 +780,13 @@ static inline void filterNodesInLayoutAtIndexesWithIntersectingNodes(
 
 - (BOOL)usesImplicitHierarchyManagement
 {
+  ASDN::MutexLocker l(_propertyLock);
   return _usesImplicitHierarchyManagement ?: [[self class] usesImplicitHierarchyManagement];
 }
 
 - (void)setUsesImplicitHierarchyManagement:(BOOL)value
 {
+  ASDN::MutexLocker l(_propertyLock);
   _usesImplicitHierarchyManagement = value;
 }
 
@@ -1718,7 +1720,7 @@ static NSInteger incrementIfFound(NSInteger i) {
         [self _tearDownPlaceholderLayer];
       };
 
-      if (_placeholderFadeDuration > 0.0) {
+      if (_placeholderFadeDuration > 0.0 && ASInterfaceStateIncludesVisible(self.interfaceState)) {
         [CATransaction begin];
         [CATransaction setCompletionBlock:cleanupBlock];
         [CATransaction setAnimationDuration:_placeholderFadeDuration];