Update gentest to account for box sizing (#1700)

Summary:
Pull Request resolved: https://github.com/facebook/yoga/pull/1700

tsia, need to teach gentest to write box sizing now.

Reviewed By: NickGerleman

Differential Revision: D63138372

fbshipit-source-id: 29072b3e602fe77edb14a8857a83e5bba4c92205

gentest/gentest-cpp.js

@@ -136,6 +136,9 @@ CPPEmitter.prototype = Object.create(Emitter.prototype, {
   YGWrapWrap: {value: 'YGWrapWrap'},
   YGWrapWrapReverse: {value: 'YGWrapWrapReverse'},
 
+  YGBoxSizingBorderBox: {value: 'YGBoxSizingBorderBox'},
+  YGBoxSizingContentBox: {value: 'YGBoxSizingContentBox'},
+
   YGUndefined: {value: 'YGUndefined'},
 
   YGDisplayFlex: {value: 'YGDisplayFlex'},
@@ -512,6 +515,14 @@ CPPEmitter.prototype = Object.create(Emitter.prototype, {
     },
   },
 
+  YGNodeStyleSetBoxSizing: {
+    value: function (nodeName, value) {
+      this.push(
+        'YGNodeStyleSetBoxSizing(' + nodeName + ', ' + toValueCpp(value) + ');',
+      );
+    },
+  },
+
   YGNodeSetMeasureFunc: {
     value: function (nodeName, innerText) {
       this.push(`YGNodeSetContext(${nodeName}, (void*)"${innerText}");`);