The total flex factores need to be a minimum of 1 if any

Summary:
The only thing I found in the spec for this change is the following. Not exactly sure if this is the thing this PR is about:

> For each flex item, subtract its outer flex base size from its max-content contribution size. If that result is not zero, divide it by (if the result was positive) its **flex grow factor floored at 1** or (if the result was negative) by its scaled flex shrink factor, having **floored the flex shrink factor at 1**. This is the item’s max-content flex fraction.

But at least it seems a required change.

Fixes facebook/yoga#566
Closes https://github.com/facebook/yoga/pull/572

Differential Revision: D5264388

Pulled By: emilsjolander

fbshipit-source-id: 0004d1c3b9bad070a98cd6766c1adc06a54475f8

yoga/Yoga.c

@@ -2278,6 +2278,16 @@ static void YGNodelayoutImpl(const YGNodeRef node,
       }
     }
 
+    // The total flex factor needs to be floored to 1.
+    if (totalFlexGrowFactors > 0 && totalFlexGrowFactors < 1) {
+      totalFlexGrowFactors = 1;
+    }
+
+    // The total flex shrink factor needs to be floored to 1.
+    if (totalFlexShrinkScaledFactors > 0 && totalFlexShrinkScaledFactors < 1) {
+      totalFlexShrinkScaledFactors = 1;
+    }
+
     // If we don't need to measure the cross axis, we can skip the entire flex
     // step.
     const bool canSkipFlex = !performLayout && measureModeCrossDim == YGMeasureModeExactly;