Fix naming convetion:

- "Layout node" is changed to "layout spec".
- Update tests.
- Update Kittens sample.

AsyncDisplayKit/Layout/ASOverlayLayoutSpec.mm

@@ -0,0 +1,55 @@
+/*
+ *  Copyright (c) 2014-present, Facebook, Inc.
+ *  All rights reserved.
+ *
+ *  This source code is licensed under the BSD-style license found in the
+ *  LICENSE file in the root directory of this source tree. An additional grant
+ *  of patent rights can be found in the PATENTS file in the same directory.
+ *
+ */
+
+#import "ASOverlayLayoutSpec.h"
+
+#import "ASAssert.h"
+#import "ASBaseDefines.h"
+
+@implementation ASOverlayLayoutSpec
+{
+  id<ASLayoutable> _overlay;
+  id<ASLayoutable> _child;
+}
+
++ (instancetype)newWithChild:(id<ASLayoutable>)child overlay:(id<ASLayoutable>)overlay
+{
+  ASOverlayLayoutSpec *spec = [super new];
+  if (spec) {
+    ASDisplayNodeAssertNotNil(child, @"Child that will be overlayed on shouldn't be nil");
+    spec->_overlay = overlay;
+    spec->_child = child;
+  }
+  return spec;
+}
+
++ (instancetype)new
+{
+  ASDISPLAYNODE_NOT_DESIGNATED_INITIALIZER();
+}
+
+/**
+ First layout the contents, then fit the overlay on top of it.
+ */
+- (ASLayout *)calculateLayoutThatFits:(ASSizeRange)constrainedSize
+{
+  ASLayout *contentsLayout = [_child calculateLayoutThatFits:constrainedSize];
+  contentsLayout.position = CGPointZero;
+  NSMutableArray *layoutChildren = [NSMutableArray arrayWithObject:contentsLayout];
+  if (_overlay) {
+    ASLayout *overlayLayout = [_overlay calculateLayoutThatFits:{contentsLayout.size, contentsLayout.size}];
+    overlayLayout.position = CGPointZero;
+    [layoutChildren addObject:overlayLayout];
+  }
+  
+  return [ASLayout newWithLayoutableObject:self size:contentsLayout.size children:layoutChildren];
+}
+
+@end