BREAKING: remove css_sizeThatFits:, replace with new API.

Summary: When I try to use this in practice, I have come to realize that css_sizeThatFits will 99% return to you the constrainedSize that you pass it, thus making it useless. Instead, we replace it with a new API that will tell you the optimal size of the resolved layout. From this we can choose to use that size, or scale it down.

Reviewed By: emilsjolander

Differential Revision: D4191873

fbshipit-source-id: d36a2850448d9d82f97e5ef4c7397778c2a14094

CSSLayoutKit/UIView+CSSLayout.m

@@ -157,32 +157,21 @@
   return CSSNodeLayoutGetDirection([self cssNode]);
 }
 
-- (CGSize)css_sizeThatFits:(CGSize)constrainedSize
-{
-  NSAssert([NSThread isMainThread], @"CSS Layout calculation must be done on main.");
-  NSAssert([self css_usesFlexbox], @"CSS Layout is not enabled for this view.");
-
-  CSSAttachNodesFromViewHierachy(self);
-
-  const CSSNodeRef node = [self cssNode];
-  CSSNodeCalculateLayout(
-    node,
-    constrainedSize.width,
-    constrainedSize.height,
-    CSSNodeStyleGetDirection(node));
-
-  return (CGSize) {
-    .width = CSSNodeLayoutGetWidth(node),
-    .height = CSSNodeLayoutGetHeight(node),
-  };
-}
-
 - (void)css_applyLayout
 {
-  [self css_sizeThatFits:self.bounds.size];
+  [self calculateLayoutWithSize:self.bounds.size];
   CSSApplyLayoutToViewHierarchy(self);
 }
 
+- (CGSize)css_intrinsicSize
+{
+  const CGSize constrainedSize = {
+      .width = CSSUndefined,
+      .height = CSSUndefined,
+  };
+  return [self calculateLayoutWithSize:constrainedSize];
+}
+
 #pragma mark - Private
 
 - (CSSNodeRef)cssNode
@@ -197,6 +186,26 @@
   return node.cnode;
 }
 
+- (CGSize)calculateLayoutWithSize:(CGSize)size
+{
+  NSAssert([NSThread isMainThread], @"CSS Layout calculation must be done on main.");
+  NSAssert([self css_usesFlexbox], @"CSS Layout is not enabled for this view.");
+
+  CSSAttachNodesFromViewHierachy(self);
+
+  const CSSNodeRef node = [self cssNode];
+  CSSNodeCalculateLayout(
+    node,
+    size.width,
+    size.height,
+    CSSNodeStyleGetDirection(node));
+
+  return (CGSize) {
+    .width = CSSNodeLayoutGetWidth(node),
+    .height = CSSNodeLayoutGetHeight(node),
+  };
+}
+
 static CSSSize CSSMeasureView(
   CSSNodeRef node,
   float width,