support flexible top container

Summary:
The main container that gets called `applyLayoutPreservingOrigin:` is using its size as a fixed bounding box.
In some cases it's preferrable to let it accomodate its contents.

This diffs extends `applyLayoutPreservingOrigin:` by adding an additional parameter which can be used to sepecify whether width and/or height are fixed or flexible.

Feel free to suggest better names than `YGDimensionFlexibility` & co.
Let me know if you prefet to kill the API without flexiblity specifier - I'll codemod everything then.

Reviewed By: dshahidehpour

Differential Revision: D4929702

fbshipit-source-id: f128f244140b4a54d8ce3b3f4edddbb9756f8fdf

YogaKit/Source/YGLayout.h

@@ -10,6 +10,11 @@
 #import <UIKit/UIKit.h>
 #import <yoga/YGEnums.h>
 
+typedef NS_OPTIONS(NSInteger, YGDimensionFlexibility) {
+  YGDimensionFlexibilityFlexibleWidth = 1 << 0,
+  YGDimensionFlexibilityFlexibleHeigth = 1 << 1,
+};
+
 @interface YGLayout : NSObject
 
 /**
@@ -95,6 +100,13 @@
 - (void)applyLayoutPreservingOrigin:(BOOL)preserveOrigin
     NS_SWIFT_NAME(applyLayout(preservingOrigin:));
 
+/**
+ Perform a layout calculation and update the frames of the views in the hierarchy with the results.
+ If the origin is not preserved, the root view's layout results will applied from {0,0}.
+ */
+- (void)applyLayoutPreservingOrigin:(BOOL)preserveOrigin dimensionFlexibility:(YGDimensionFlexibility)dimensionFlexibility
+    NS_SWIFT_NAME(applyLayout(preservingOrigin:dimensionFlexibility:));
+
 /**
  Returns the size of the view if no constraints were given. This could equivalent to calling [self
  sizeThatFits:CGSizeMake(CGFLOAT_MAX, CGFLOAT_MAX)];

YogaKit/Source/YGLayout.m

@@ -235,6 +235,20 @@ YG_PROPERTY(CGFloat, aspectRatio, AspectRatio)
   YGApplyLayoutToViewHierarchy(self.view, preserveOrigin);
 }
 
+- (void)applyLayoutPreservingOrigin:(BOOL)preserveOrigin dimensionFlexibility:(YGDimensionFlexibility)dimensionFlexibility
+{
+  CGSize size = self.view.bounds.size;
+  if (dimensionFlexibility & YGDimensionFlexibilityFlexibleWidth) {
+    size.width = YGUndefined;
+  }
+  if (dimensionFlexibility & YGDimensionFlexibilityFlexibleHeigth) {
+    size.height = YGUndefined;
+  }
+  [self calculateLayoutWithSize:size];
+  YGApplyLayoutToViewHierarchy(self.view, NO);
+}
+
+
 - (CGSize)intrinsicSize
 {
   const CGSize constrainedSize = {