Fix naming convetion:

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

AsyncDisplayKit/Layout/ASBackgroundLayoutSpec.mm

@@ -0,0 +1,61 @@
+/*
+ *  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 "ASBackgroundLayoutSpec.h"
+
+#import "ASAssert.h"
+#import "ASBaseDefines.h"
+
+@interface ASBackgroundLayoutSpec ()
+{
+  id<ASLayoutable> _child;
+  id<ASLayoutable> _background;
+}
+@end
+
+@implementation ASBackgroundLayoutSpec
+
++ (instancetype)newWithChild:(id<ASLayoutable>)child background:(id<ASLayoutable>)background
+{
+  if (child == nil) {
+    return nil;
+  }
+  ASBackgroundLayoutSpec *spec = [super new];
+  spec->_child = child;
+  spec->_background = background;
+  return spec;
+}
+
++ (instancetype)new
+{
+  ASDISPLAYNODE_NOT_DESIGNATED_INITIALIZER();
+}
+
+/**
+ First layout the contents, then fit the background image.
+ */
+- (ASLayout *)calculateLayoutThatFits:(ASSizeRange)constrainedSize
+{
+  ASLayout *contentsLayout = [_child calculateLayoutThatFits:constrainedSize];
+  contentsLayout.position = CGPointZero;
+
+  NSMutableArray *children = [NSMutableArray arrayWithCapacity:2];
+  if (_background) {
+    // Size background to exactly the same size.
+    ASLayout *backgroundLayout = [_background calculateLayoutThatFits:{contentsLayout.size, contentsLayout.size}];
+    backgroundLayout.position = CGPointZero;
+    [children addObject:backgroundLayout];
+  }
+  [children addObject:contentsLayout];
+
+  return [ASLayout newWithLayoutableObject:self size:contentsLayout.size children:children];
+}
+
+@end