Fix SingleFlex Child condition

Summary:
Fixes the improper `singleFlexChild` optimization. In the case when all the childs have `flex-grow:0 flex-grow:0` except one child with `flex-grow:1 flex-shrink:1`, then one can simply measure all the non-flexing children and then give the flexing child all the remaining space.

Also added a test case which reproduced the bug

Reviewed By: IanChilds

Differential Revision: D8782684

fbshipit-source-id: ffd4d35b6122f82111b987540efb23bd2a8da5a2

Author: priteshrnandgaonkar

ReactCommon/yoga/yoga/Yoga.cpp

@@ -1788,16 +1788,17 @@ static void YGNodeComputeFlexBasisForChildren(
   // child to exactly match the remaining space
   if (measureModeMainDim == YGMeasureModeExactly) {
     for (auto child : children) {
-      if (singleFlexChild != nullptr) {
-        if (child->isNodeFlexible()) {
-          // There is already a flexible child, abort
+      if (child->isNodeFlexible()) {
+        if (singleFlexChild != nullptr ||
+            YGFloatsEqual(child->resolveFlexGrow(), 0.0f) ||
+            YGFloatsEqual(child->resolveFlexShrink(), 0.0f)) {
+          // There is already a flexible child, or this flexible child doesn't
+          // have flexGrow and flexShrink, abort
           singleFlexChild = nullptr;
           break;
+        } else {
+          singleFlexChild = child;
         }
-      } else if (
-          child->resolveFlexGrow() > 0.0f &&
-          child->resolveFlexShrink() > 0.0f) {
-        singleFlexChild = child;
       }
     }
   }