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

java/com/facebook/yoga/YogaNode.java

@@ -378,6 +378,12 @@ public class YogaNode implements YogaNodeAPI<YogaNode> {
     jni_YGNodeStyleSetFlexBasisPercent(mNativePointer, percent);
   }
 
+  private native void jni_YGNodeStyleSetFlexBasisAuto(long nativePointer);
+  @Override
+  public void setFlexBasisAuto() {
+    jni_YGNodeStyleSetFlexBasisAuto(mNativePointer);
+  }
+
   private native Object jni_YGNodeStyleGetMargin(long nativePointer, int edge);
   @Override
   public YogaValue getMargin(YogaEdge edge) {
@@ -401,6 +407,13 @@ public class YogaNode implements YogaNodeAPI<YogaNode> {
     jni_YGNodeStyleSetMarginPercent(mNativePointer, edge.intValue(), percent);
   }
 
+  private native void jni_YGNodeStyleSetMarginAuto(long nativePointer, int edge);
+  @Override
+  public void setMarginAuto(YogaEdge edge) {
+    mHasSetMargin = true;
+    jni_YGNodeStyleSetMarginAuto(mNativePointer, edge.intValue());
+  }
+
   private native Object jni_YGNodeStyleGetPadding(long nativePointer, int edge);
   @Override
   public YogaValue getPadding(YogaEdge edge) {
@@ -481,6 +494,12 @@ public class YogaNode implements YogaNodeAPI<YogaNode> {
     jni_YGNodeStyleSetWidthPercent(mNativePointer, percent);
   }
 
+  private native void jni_YGNodeStyleSetWidthAuto(long nativePointer);
+  @Override
+  public void setWidthAuto() {
+    jni_YGNodeStyleSetWidthAuto(mNativePointer);
+  }
+
   private native Object jni_YGNodeStyleGetHeight(long nativePointer);
   @Override
   public YogaValue getHeight() {
@@ -499,6 +518,12 @@ public class YogaNode implements YogaNodeAPI<YogaNode> {
     jni_YGNodeStyleSetHeightPercent(mNativePointer, percent);
   }
 
+  private native void jni_YGNodeStyleSetHeightAuto(long nativePointer);
+  @Override
+  public void setHeightAuto() {
+    jni_YGNodeStyleSetHeightAuto(mNativePointer);
+  }
+
   private native Object jni_YGNodeStyleGetMinWidth(long nativePointer);
   @Override
   public YogaValue getMinWidth() {

java/com/facebook/yoga/YogaNodeAPI.java

@@ -49,9 +49,11 @@ public interface YogaNodeAPI<YogaNodeType extends YogaNodeAPI> {
   YogaValue getFlexBasis();
   void setFlexBasis(float flexBasis);
   void setFlexBasisPercent(float percent);
+  void setFlexBasisAuto();
   YogaValue getMargin(YogaEdge edge);
   void setMargin(YogaEdge edge, float margin);
   void setMarginPercent(YogaEdge edge, float percent);
+  void setMarginAuto(YogaEdge edge);
   YogaValue getPadding(YogaEdge edge);
   void setPadding(YogaEdge edge, float padding);
   void setPaddingPercent(YogaEdge edge, float percent);
@@ -63,9 +65,11 @@ public interface YogaNodeAPI<YogaNodeType extends YogaNodeAPI> {
   YogaValue getWidth();
   void setWidth(float width);
   void setWidthPercent(float percent);
+  void setWidthAuto();
   YogaValue getHeight();
   void setHeight(float height);
   void setHeightPercent(float percent);
+  void setHeightAuto();
   YogaValue getMaxWidth();
   void setMaxWidth(float maxWidth);
   void setMaxWidthPercent(float percent);

java/com/facebook/yoga/YogaUnit.java

@@ -15,7 +15,8 @@ import com.facebook.proguard.annotations.DoNotStrip;
 public enum YogaUnit {
   UNDEFINED(0),
   PIXEL(1),
-  PERCENT(2);
+  PERCENT(2),
+  AUTO(3);
 
   private int mIntValue;
 
@@ -32,6 +33,7 @@ public enum YogaUnit {
       case 0: return UNDEFINED;
       case 1: return PIXEL;
       case 2: return PERCENT;
+      case 3: return AUTO;
       default: throw new IllegalArgumentException("Unknown enum value: " + value);
     }
   }