Bug 1654541 - fit-content percentage should only clamp when definite. r=emilio,layout-grid-reviewers,TYLin

Differential Revision: https://phabricator.services.mozilla.com/D226204

layout/generic/nsGridContainerFrame.cpp

@@ -449,7 +449,9 @@ TrackSize::StateBits nsGridContainerFrame::TrackSize::Initialize(
   if (aSize.IsFitContent()) {
     // In layout, fit-content(size) behaves as minmax(auto, max-content), with
     // 'size' as an additional upper-bound.
-    mState = eFitContent;
+    if (!::IsPercentOfIndefiniteSize(aSize.AsFitContent(), aPercentageBasis)) {
+      mState = eFitContent;
+    }
     minSizeTag = Tag::Auto;
     maxSizeTag = Tag::MaxContent;
   }