Bug 1313421 part 1: Unconditionally cache a FlexItem's ascent, after it's been reflowed. r=mats

This removes a (very minor) optimization. The optimization was simply that we
avoided storing this nscoord value, if we could tell that we weren't ever going
to need it. Now it's becoming a bit more complicated to prove that we'll never
need it, so we might as well just store it unconditionally.

MozReview-Commit-ID: 94FFc9SO516

layout/generic/nsFlexContainerFrame.cpp

@@ -1645,14 +1645,7 @@ nsFlexContainerFrame::
                     0, 0, flags);
 
   aFlexItem.SetHadMeasuringReflow();
-
-  // If this is the first child, save its ascent, since it may be what
-  // establishes the container's baseline. Also save the ascent if this child
-  // needs to be baseline-aligned. (Else, we don't care about ascent/baseline.)
-  if (aFlexItem.Frame() == mFrames.FirstChild() ||
-      aFlexItem.GetAlignSelf() == NS_STYLE_ALIGN_BASELINE) {
-    aFlexItem.SetAscent(childDesiredSize.BlockStartAscent());
-  }
+  aFlexItem.SetAscent(childDesiredSize.BlockStartAscent());
 
   // Subtract border/padding in vertical axis, to get _just_
   // the effective computed value of the "height" property.
@@ -3782,13 +3775,7 @@ nsFlexContainerFrame::SizeItemInCrossAxis(
     aItem.SetCrossSize(childDesiredSize.Height() - crossAxisBorderPadding);
   }
 
-  // If this is the first child, save its ascent, since it may be what
-  // establishes the container's baseline. Also save the ascent if this child
-  // needs to be baseline-aligned. (Else, we don't care about baseline/ascent.)
-  if (aItem.Frame() == mFrames.FirstChild() ||
-      aItem.GetAlignSelf() == NS_STYLE_ALIGN_BASELINE) {
-    aItem.SetAscent(childDesiredSize.BlockStartAscent());
-  }
+  aItem.SetAscent(childDesiredSize.BlockStartAscent());
 }
 
 void
@@ -4451,10 +4438,7 @@ nsFlexContainerFrame::ReflowFlexItem(nsPresContext* aPresContext,
                     childDesiredSize, &childReflowInput,
                     outerWM, aFramePos, aContainerSize, 0);
 
-  // Save the first child's ascent; it may establish container's baseline.
-  if (aItem.Frame() == mFrames.FirstChild()) {
-    aItem.SetAscent(childDesiredSize.BlockStartAscent());
-  }
+  aItem.SetAscent(childDesiredSize.BlockStartAscent());
 }
 
 /* virtual */ nscoord