Clean up #468:

- -layoutSpecThatFits: must return an ASLayoutSpec.
- Move ASDisplayNode's -measureWithSizeRange: redeclaration to ASDisplayNode.h.
- Rename ASStackLayoutChild.h to ASStackLayoutDefines.h.
- Rename ASStaticLayoutSpecDimension.h to ASRelativeSize.h.
- Don't import ASLayout.h in other headers to prevent circular inclusions.
- Explain use cases of ASLayout's initializers.
- Clean up ASInternalHelpers.h.

AsyncDisplayKit/Layout/ASRelativeSize.h

@@ -0,0 +1,73 @@
+/*
+ *  Copyright (c) 2015-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 <UIKit/UIKit.h>
+#import <AsyncDisplayKit/ASBaseDefines.h>
+#import <AsyncDisplayKit/ASDimension.h>
+
+/** 
+ Expresses a size with relative dimensions.
+ Used by ASStaticLayoutSpec.
+ */
+typedef struct {
+  ASRelativeDimension width;
+  ASRelativeDimension height;
+} ASRelativeSize;
+
+/**
+ Expresses an inclusive range of relative sizes. Used to provide additional constraint to layout. 
+ Used by ASStaticLayoutSpec.
+ */
+typedef struct {
+  ASRelativeSize min;
+  ASRelativeSize max;
+} ASRelativeSizeRange;
+
+extern ASRelativeSizeRange const ASRelativeSizeRangeUnconstrained;
+
+ASDISPLAYNODE_EXTERN_C_BEGIN
+
+#pragma mark -
+#pragma mark ASRelativeSize
+
+extern ASRelativeSize ASRelativeSizeMake(ASRelativeDimension width, ASRelativeDimension height);
+
+/** Convenience constructor to provide size in Points. */
+extern ASRelativeSize ASRelativeSizeMakeWithCGSize(CGSize size);
+
+/** Resolve this relative size relative to a parent size. */
+extern CGSize ASRelativeSizeResolve(ASRelativeSize relativeSize, CGSize parentSize);
+
+extern BOOL ASRelativeSizeEqualToRelativeSize(ASRelativeSize lhs, ASRelativeSize rhs);
+
+extern NSString *NSStringFromASRelativeSize(ASRelativeSize size);
+
+#pragma mark -
+#pragma mark ASRelativeSizeRange
+
+extern ASRelativeSizeRange ASRelativeSizeRangeMake(ASRelativeSize min, ASRelativeSize max);
+
+#pragma mark Convenience constructors to provide an exact size (min == max).
+extern ASRelativeSizeRange ASRelativeSizeRangeMakeWithExactRelativeSize(ASRelativeSize exact);
+
+extern ASRelativeSizeRange ASRelativeSizeRangeMakeWithExactCGSize(CGSize exact);
+
+extern ASRelativeSizeRange ASRelativeSizeRangeMakeWithExactRelativeDimensions(ASRelativeDimension exactWidth,
+                                                                              ASRelativeDimension exactHeight);
+
+extern BOOL ASRelativeSizeRangeEqualToRelativeSizeRange(ASRelativeSizeRange lhs, ASRelativeSizeRange rhs);
+
+/**
+ Provided a parent size, compute final dimensions for this RelativeSizeRange to arrive at a SizeRange.
+ */
+extern ASSizeRange ASRelativeSizeRangeResolve(ASRelativeSizeRange relativeSizeRange,
+                                                       CGSize parentSize);
+
+ASDISPLAYNODE_EXTERN_C_END