Bug 1269046 part 9: Add a flag to control whether CSSAlignUtils::AlignJustifySelf() expands "auto" margins. r=mats

MozReview-Commit-ID: I0UdEIfiOqX

layout/generic/CSSAlignUtils.cpp

@@ -84,10 +84,14 @@ CSSAlignUtils::AlignJustifySelf(uint8_t aAlignment, LogicalAxis aAxis,
   const auto& styleMargin = aRI.mStyleMargin->mMargin;
   bool hasAutoMarginStart;
   bool hasAutoMarginEnd;
-  if (aAxis == eLogicalAxisBlock) {
+  if (aFlags & AlignJustifyFlags::eIgnoreAutoMargins) {
+    // (Note: ReflowInput will have treated "auto" margins as 0, so we
+    // don't need to do anything special to avoid expanding them.)
+    hasAutoMarginStart = hasAutoMarginEnd = false;
+  } else if (aAxis == eLogicalAxisBlock) {
     hasAutoMarginStart = styleMargin.GetBStartUnit(wm) == eStyleUnit_Auto;
     hasAutoMarginEnd = styleMargin.GetBEndUnit(wm) == eStyleUnit_Auto;
-  } else {
+  } else { /* aAxis == eLogicalAxisInline */
     hasAutoMarginStart = styleMargin.GetIStartUnit(wm) == eStyleUnit_Auto;
     hasAutoMarginEnd = styleMargin.GetIEndUnit(wm) == eStyleUnit_Auto;
   }

layout/generic/CSSAlignUtils.h

@@ -24,6 +24,10 @@ public:
     // Indicates that the container's start side in aAxis is the same
     // as the child's start side in the child's parallel axis.
     eSameSide          = 1 << 1,
+    // Indicates that AlignJustifySelf() shouldn't expand "auto" margins.
+    // (By default, AlignJustifySelf() *will* expand such margins, to fill the
+    // available space before any alignment is done.)
+    eIgnoreAutoMargins = 1 << 2,
   };
 
   /**

layout/generic/nsAbsoluteContainingBlock.cpp

@@ -423,7 +423,7 @@ OffsetToAlignedStaticPos(const ReflowInput& aKidReflowInput,
     ? alignAreaSize.ISize(pcWM)
     : alignAreaSize.BSize(pcWM);
 
-  AlignJustifyFlags flags = AlignJustifyFlags::eNoFlags;
+  AlignJustifyFlags flags = AlignJustifyFlags::eIgnoreAutoMargins;
   uint16_t alignConst =
     aPlaceholderContainer->CSSAlignmentForAbsPosChild(aKidReflowInput, pcAxis);
   // XXXdholbert: Handle <overflow-position> in bug 1311892 (by conditionally