For flex items, percent paddings should resolve against their respective dimension

Source/core/rendering/RenderBoxModelObject.cpp

Index: Source/core/rendering/RenderBoxModelObject.cpp
diff --git a/Source/core/rendering/RenderBoxModelObject.cpp b/Source/core/rendering/RenderBoxModelObject.cpp
index d8e6b964a86ff8542c214b0063fbfc997faca326..063f480b0453c4ea07fb125489b92f9e1490d477 100644
--- a/Source/core/rendering/RenderBoxModelObject.cpp
+++ b/Source/core/rendering/RenderBoxModelObject.cpp
@@ -312,11 +312,19 @@ int RenderBoxModelObject::pixelSnappedOffsetHeight() const
     return snapSizeToPixel(offsetHeight(), offsetTop());
 }
 
-LayoutUnit RenderBoxModelObject::computedCSSPadding(const Length& padding) const
+LayoutUnit RenderBoxModelObject::computedCSSPadding(const Length& padding, PaddingType type) const
 {
     LayoutUnit w = 0;
-    if (padding.isPercent())
-        w = containingBlockLogicalWidthForContent();
+    if (padding.isPercent()) {
+        if (containingBlock()->isFlexibleBox() && RuntimeEnabledFeatures::verticalPaddingEnabled()) {
+            if (type == TopPadding || type == BottomPadding || type == BeforePadding || type == AfterPadding)
+                w = containingBlockLogicalHeightForPadding();
+            else
+                w = containingBlockLogicalWidthForContent();
+        } else {
+            w = containingBlockLogicalWidthForContent();
+        }
+    }
     return minimumValueForLength(padding, w);
 }
 
@@ -2503,6 +2511,32 @@ LayoutUnit RenderBoxModelObject::containingBlockLogicalWidthForContent() const
     return containingBlock()->availableLogicalWidth();
 }
 
+LayoutUnit RenderBoxModelObject::containingBlockLogicalHeightForPadding() const
+{
+    switch (containingBlock()->style()->logicalHeight().type()) {
+    case Auto:
+    case MinContent:
+    case MaxContent:
+    case FitContent:
+    case FillAvailable:
+    case Intrinsic:
+    case MinIntrinsic:
+    case MaxSizeNone:
+    case ExtendToZoom:
+    case DeviceWidth:
+    case DeviceHeight:
+        return 0;
+    case Fixed:
+    case Calculated:
+        return containingBlock()->style()->logicalHeight().value();
+    case Percent:
+        return std::max<LayoutUnit>(containingBlock()->computePercentageLogicalHeight(containingBlock()->style()->logicalHeight()), 0);
+    }
+
+    ASSERT_NOT_REACHED();
+    return 0;
+}
+
 RenderBoxModelObject* RenderBoxModelObject::continuation() const
 {
     if (!continuationMap)