Add constructor in YGLayout

Summary: Add default constructor in YGLayout and moved to separate file. This diff also addresses https://github.com/facebook/yoga/pull/700

Reviewed By: emilsjolander

Differential Revision: D7019653

fbshipit-source-id: 5a2655626db0915fcebe7d4517e2d0b2e2484460

yoga/YGStyle.cpp

@@ -8,6 +8,27 @@
  */
 #include "YGStyle.h"
 
+const YGValue kYGValueUndefined = {YGUndefined, YGUnitUndefined};
+
+const YGValue kYGValueAuto = {YGUndefined, YGUnitAuto};
+
+const std::array<YGValue, YGEdgeCount> kYGDefaultEdgeValuesUnit = {
+    {kYGValueUndefined,
+     kYGValueUndefined,
+     kYGValueUndefined,
+     kYGValueUndefined,
+     kYGValueUndefined,
+     kYGValueUndefined,
+     kYGValueUndefined,
+     kYGValueUndefined,
+     kYGValueUndefined}};
+
+const std::array<YGValue, 2> kYGDefaultDimensionValuesAutoUnit = {
+    {kYGValueAuto, kYGValueAuto}};
+
+const std::array<YGValue, 2> kYGDefaultDimensionValuesUnit = {
+    {kYGValueUndefined, kYGValueUndefined}};
+
 YGStyle::YGStyle()
     : direction(YGDirectionInherit),
       flexDirection(YGFlexDirectionColumn),