Bug 1298008 Part 3: Update ReflowInput::CalculateBlockSideMargins to store computed values in the UsedMargin property. r=dholbert

MozReview-Commit-ID: 74u7rFkiVln

--HG--
extra : rebase_source : 896f1ee98c78d94ea47c4a11ba87d4f516d0319e

layout/generic/ReflowInput.cpp

@@ -2531,7 +2531,7 @@ static void
 UpdateProp(nsIFrame* aFrame,
            const FramePropertyDescriptor<nsMargin>* aProperty,
            bool aNeeded,
-           nsMargin& aNewValue)
+           const nsMargin& aNewValue)
 {
   if (aNeeded) {
     nsMargin* propValue = aFrame->GetProperty(aProperty);
@@ -2566,10 +2566,10 @@ SizeComputationInput::InitOffsets(WritingMode aWM,
   // XXX fix to provide 0,0 for the top&bottom margins for
   // inline-non-replaced elements
   bool needMarginProp = ComputeMargin(aWM, aPercentBasis);
-  // XXX We need to include 'auto' horizontal margins in this too!
-  // ... but if we did that, we'd need to fix nsFrame::GetUsedMargin
-  // to use it even when the margins are all zero (since sometimes
-  // they get treated as auto)
+  // Note that ComputeMargin() simplistically resolves 'auto' margins to 0.
+  // In formatting contexts where this isn't correct, some later code will
+  // need to update the UsedMargin() property with the actual resolved value.
+  // One example of this is ::CalculateBlockSideMargins().
   ::UpdateProp(mFrame, nsIFrame::UsedMarginProperty(), needMarginProp,
                ComputedPhysicalMargin());
 
@@ -2800,7 +2800,16 @@ ReflowInput::CalculateBlockSideMargins(LayoutFrameType aFrameType)
   } else if (isAutoEndMargin) {
     margin.IEnd(cbWM) += availMarginSpace;
   }
-  SetComputedLogicalMargin(margin.ConvertTo(mWritingMode, cbWM));
+  LogicalMargin marginInOurWM = margin.ConvertTo(mWritingMode, cbWM);
+  SetComputedLogicalMargin(marginInOurWM);
+
+  if (isAutoStartMargin || isAutoEndMargin) {
+    // Update the UsedMargin property if we were tracking it already.
+    nsMargin* propValue = mFrame->GetProperty(nsIFrame::UsedMarginProperty());
+    if (propValue) {
+      *propValue = marginInOurWM.GetPhysicalMargin(mWritingMode);
+    }
+  }
 }
 
 #define NORMAL_LINE_HEIGHT_FACTOR 1.2f    // in term of emHeight