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/Tests/YogaKitTests.m

@@ -154,6 +154,54 @@
   XCTAssertEqual(25, view2.frame.origin.y);
 }
 
+- (void)testContainerWithFlexibleWidthGetsCorrectlySized
+{
+  UIView *container = [[UIView alloc] initWithFrame:CGRectMake(0,0,200,200)];
+  container.yoga.isEnabled = YES;
+
+  UIView *view = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 100, 100)];
+  view.yoga.isEnabled = YES;
+  view.yoga.width = 100;
+  view.yoga.height = 100;
+  [container addSubview:view];
+
+  [container.yoga applyLayoutPreservingOrigin:YES dimensionFlexibility:YGDimensionFlexibilityFlexibleWidth];
+  XCTAssertEqual(100, container.frame.size.width);
+  XCTAssertEqual(200, container.frame.size.height);
+}
+
+- (void)testContainerWithFlexibleHeightGetsCorrectlySized
+{
+  UIView *container = [[UIView alloc] initWithFrame:CGRectMake(0,0,200,200)];
+  container.yoga.isEnabled = YES;
+
+  UIView *view = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 100, 100)];
+  view.yoga.isEnabled = YES;
+  view.yoga.width = 100;
+  view.yoga.height = 100;
+  [container addSubview:view];
+
+  [container.yoga applyLayoutPreservingOrigin:YES dimensionFlexibility:YGDimensionFlexibilityFlexibleHeigth];
+  XCTAssertEqual(200, container.frame.size.width);
+  XCTAssertEqual(100, container.frame.size.height);
+}
+
+- (void)testContainerWithFlexibleWidthAndHeightGetsCorrectlySized
+{
+  UIView *container = [[UIView alloc] initWithFrame:CGRectMake(0,0,200,200)];
+  container.yoga.isEnabled = YES;
+
+  UIView *view = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 100, 100)];
+  view.yoga.isEnabled = YES;
+  view.yoga.width = 100;
+  view.yoga.height = 100;
+  [container addSubview:view];
+
+  [container.yoga applyLayoutPreservingOrigin:YES dimensionFlexibility:YGDimensionFlexibilityFlexibleWidth | YGDimensionFlexibilityFlexibleHeigth];
+  XCTAssertEqual(100, container.frame.size.width);
+  XCTAssertEqual(100, container.frame.size.height);
+}
+
 - (void)testMarkingDirtyOnlyWorksOnLeafNodes
 {
   UIView *container = [[UIView alloc] initWithFrame:CGRectZero];