Implementation of operator== for YGValue

Summary:
@public
It's very useful sometimes for product code to compare `YGValue`s (e.g. in Fabric).

Reviewed By: priteshrnandgaonkar

Differential Revision: D8937594

fbshipit-source-id: b93e1ab4a6419ada6746f233b587e8c9cb32c6d4

Author: shergin

ReactCommon/yoga/yoga/Yoga.cpp

@@ -48,6 +48,19 @@ const YGValue YGValueZero = {0, YGUnitPoint};
 const YGValue YGValueUndefined = {YGUndefined, YGUnitUndefined};
 const YGValue YGValueAuto = {YGUndefined, YGUnitAuto};
 
+bool operator==(const YGValue& lhs, const YGValue& rhs) {
+  if ((lhs.unit == YGUnitUndefined && rhs.unit == YGUnitUndefined) ||
+      (lhs.unit == YGUnitAuto && rhs.unit == YGUnitAuto)) {
+    return true;
+  }
+
+  return lhs.unit == rhs.unit && lhs.value == rhs.value;
+}
+
+bool operator!=(const YGValue& lhs, const YGValue& rhs) {
+  return !(lhs == rhs);
+}
+
 #ifdef ANDROID
 #include <android/log.h>
 static int YGAndroidLog(

ReactCommon/yoga/yoga/Yoga.h

@@ -45,6 +45,13 @@ typedef struct YGValue {
 extern const YGValue YGValueUndefined;
 extern const YGValue YGValueAuto;
 
+#ifdef __cplusplus
+
+extern bool operator==(const YGValue& lhs, const YGValue& rhs);
+extern bool operator!=(const YGValue& lhs, const YGValue& rhs);
+
+#endif
+
 typedef struct YGConfig* YGConfigRef;
 
 typedef struct YGNode* YGNodeRef;