Feature auto margin

Summary:
Even so I know there are some opinions against ```margin: 0 auto``` it's still part of the spec: https://www.w3.org/TR/css-flexbox-1/#auto-margins and pretty usefull if you have to position via ```justify-content```.

This PR adds an implementation for that.

It adds an additonal ```YGUnitAuto``` and margins got ```YGNodeStyleSetMarginAuto``` functions as well.
Closes https://github.com/facebook/yoga/pull/357

Reviewed By: astreet

Differential Revision: D4501142

Pulled By: emilsjolander

fbshipit-source-id: 86519f8632496f46e78a7c9dbc5b21e212e3e0c7

javascript/sources/Node.cc

@@ -119,6 +119,11 @@ void Node::setMarginPercent(int edge, double margin)
     YGNodeStyleSetMarginPercent(m_node, static_cast<YGEdge>(edge), margin);
 }
 
+void Node::setMarginAuto(int edge)
+{
+    YGNodeStyleSetMarginAuto(m_node, static_cast<YGEdge>(edge));
+}
+
 void Node::setOverflow(int overflow)
 {
     YGNodeStyleSetOverflow(m_node, static_cast<YGOverflow>(overflow));
@@ -164,6 +169,11 @@ void Node::setWidthPercent(double width)
     YGNodeStyleSetWidthPercent(m_node, width);
 }
 
+void Node::setWidthAuto()
+{
+    YGNodeStyleSetWidthAuto(m_node);
+}
+
 void Node::setHeight(double height)
 {
     YGNodeStyleSetHeight(m_node, height);
@@ -174,6 +184,11 @@ void Node::setHeightPercent(double height)
     YGNodeStyleSetHeightPercent(m_node, height);
 }
 
+void Node::setHeightAuto()
+{
+    YGNodeStyleSetHeightAuto(m_node);
+}
+
 void Node::setMinWidth(double minWidth)
 {
     YGNodeStyleSetMinWidth(m_node, minWidth);

javascript/sources/Node.hh

@@ -65,6 +65,7 @@ class Node {
 
     void setMargin(int edge, double margin);
     void setMarginPercent(int edge, double margin);
+    void setMarginAuto(int edge);
 
     void setOverflow(int overflow);
     void setDisplay(int display);
@@ -72,13 +73,16 @@ class Node {
     void setFlex(double flex);
     void setFlexBasis(double flexBasis);
     void setFlexBasisPercent(double flexBasis);
+    void setFlexBasisAuto();
     void setFlexGrow(double flexGrow);
     void setFlexShrink(double flexShrink);
 
     void setWidth(double width);
     void setWidthPercent(double width);
+    void setWidthAuto();
     void setHeight(double height);
     void setHeightPercent(double height);
+    void setHeightAuto();
 
     void setMinWidth(double minWidth);
     void setMinWidthPercent(double minWidth);

javascript/sources/YGEnums.js

@@ -86,10 +86,11 @@ module.exports = {
   PRINT_OPTIONS_STYLE: 2,
   PRINT_OPTIONS_CHILDREN: 4,
 
-  UNIT_COUNT: 3,
+  UNIT_COUNT: 4,
   UNIT_UNDEFINED: 0,
   UNIT_PIXEL: 1,
   UNIT_PERCENT: 2,
+  UNIT_AUTO: 3,
 
   WRAP_COUNT: 2,
   WRAP_NO_WRAP: 0,

javascript/sources/entry-common.js

@@ -107,6 +107,9 @@ module.exports = function (bind, lib) {
 
                 case constants.UNIT_PERCENT:
                     return `${this.value}%`;
+                
+                case constants.UNIT_AUTO:
+                    return `auto`;
 
                 default: {
                     return `${this.value}?`;

javascript/sources/nbind.cc

@@ -65,6 +65,7 @@ NBIND_CLASS(Node)
 
     method(setMargin);
     method(setMarginPercent);
+    method(setMarginAuto);
 
     method(setOverflow);
     method(setDisplay);
@@ -77,8 +78,10 @@ NBIND_CLASS(Node)
 
     method(setWidth);
     method(setWidthPercent);
+    method(setWidthAuto);
     method(setHeight);
     method(setHeightPercent);
+    method(setHeightAuto);
 
     method(setMinWidth);
     method(setMinWidthPercent);