[Layout API] Rename ASStaticLayoutSpec to ASAbsoluteLayoutSpec (#2288)

* Rename static to absolute

* Fix examples, rename ASAbsoluteLayoutSpec class method

* rename +staticLayoutSpecWithChildren to +absoluteLayoutSpecWithChildren

* address Michael's comments

AsyncDisplayKit/Layout/ASAbsoluteLayoutSpec.mm

@@ -0,0 +1,99 @@
+//
+//  ASAbsoluteLayoutSpec.mm
+//  AsyncDisplayKit
+//
+//  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 "ASAbsoluteLayoutSpec.h"
+
+#import "ASLayoutSpecUtilities.h"
+#import "ASLayout.h"
+
+@implementation ASAbsoluteLayoutSpec
+
++ (instancetype)absoluteLayoutSpecWithChildren:(NSArray *)children
+{
+  return [[self alloc] initWithChildren:children];
+}
+
+- (instancetype)init
+{
+    return [self initWithChildren:@[]];
+}
+
+- (instancetype)initWithChildren:(NSArray *)children
+{
+  if (!(self = [super init])) {
+    return nil;
+  }
+  self.children = children;
+  return self;
+}
+
+- (ASLayout *)calculateLayoutThatFits:(ASSizeRange)constrainedSize
+{
+  // TODO: layout: isValidForLayout() call should not be necessary if INFINITY is used
+  CGSize size = {
+    (isinf(constrainedSize.max.width) || !ASPointsAreValidForLayout(constrainedSize.max.width)) ? ASLayoutableParentDimensionUndefined : constrainedSize.max.width,
+    (isinf(constrainedSize.max.height) || !ASPointsAreValidForLayout(constrainedSize.max.height)) ? ASLayoutableParentDimensionUndefined : constrainedSize.max.height
+  };
+  
+  NSArray *children = self.children;
+  NSMutableArray *sublayouts = [NSMutableArray arrayWithCapacity:children.count];
+
+  for (id<ASLayoutable> child in children) {
+    CGPoint layoutPosition = child.style.layoutPosition;
+    CGSize autoMaxSize = {
+      constrainedSize.max.width  - layoutPosition.x,
+      constrainedSize.max.height - layoutPosition.y
+    };
+
+    const ASSizeRange childConstraint = ASLayoutableSizeResolveAutoSize(child.style.size, size, {{0,0}, autoMaxSize});
+    
+    ASLayout *sublayout = [child layoutThatFits:childConstraint parentSize:size];
+    sublayout.position = layoutPosition;
+    [sublayouts addObject:sublayout];
+  }
+  
+  if (isnan(size.width)) {
+    size.width = constrainedSize.min.width;
+    for (ASLayout *sublayout in sublayouts) {
+      size.width  = MAX(size.width,  sublayout.position.x + sublayout.size.width);
+    }
+  }
+  
+  if (isnan(size.height)) {
+    size.height = constrainedSize.min.height;
+    for (ASLayout *sublayout in sublayouts) {
+      size.height = MAX(size.height, sublayout.position.y + sublayout.size.height);
+    }
+  }
+  
+  return [ASLayout layoutWithLayoutable:self size:ASSizeRangeClamp(constrainedSize, size) sublayouts:sublayouts];
+}
+
+@end
+
+@implementation ASAbsoluteLayoutSpec (ASEnvironment)
+
+- (BOOL)supportsUpwardPropagation
+{
+  return NO;
+}
+
+@end
+
+@implementation ASAbsoluteLayoutSpec (Debugging)
+
+#pragma mark - ASLayoutableAsciiArtProtocol
+
+- (NSString *)debugBoxString
+{
+  return [ASLayoutSpec asciiArtStringForChildren:self.children parentName:[self asciiArtName]];
+}
+
+@end