Correct my incorrect comments relating to combined area, and explain what combined area is for. Comment changes only. b=172896

layout/generic/nsBlockFrame.cpp

@@ -4308,7 +4308,6 @@ nsBlockFrame::PlaceLine(nsBlockReflowState& aState,
 
   nsRect combinedArea;
   aLineLayout.RelativePositionFrames(combinedArea);  // XXXldb This returned width as -15, 2001-06-12, Bugzilla
-  // XXX Changing the combined area here seems wrong. - LDB
   aLine->SetCombinedArea(combinedArea);
   if (addedBullet) {
     aLineLayout.RemoveBulletFrame(mBullet);

layout/generic/nsLineBox.h

@@ -335,7 +335,10 @@ public:
   void AppendFloaters(nsFloaterCacheFreeList& aFreeList);
   PRBool RemoveFloater(nsIFrame* aFrame);
 
-  // Combined area
+  // Combined area is the area of the line that should influence the
+  // overflow area of its parent block.  The combined area should be
+  // used for painting-related things, but should never be used for
+  // layout (except for handling of 'overflow').
   void SetCombinedArea(const nsRect& aCombinedArea);
   void GetCombinedArea(nsRect* aResult);
   PRBool CombinedAreaIntersects(const nsRect& aDamageRect) {

layout/html/base/src/nsBlockFrame.cpp

@@ -4308,7 +4308,6 @@ nsBlockFrame::PlaceLine(nsBlockReflowState& aState,
 
   nsRect combinedArea;
   aLineLayout.RelativePositionFrames(combinedArea);  // XXXldb This returned width as -15, 2001-06-12, Bugzilla
-  // XXX Changing the combined area here seems wrong. - LDB
   aLine->SetCombinedArea(combinedArea);
   if (addedBullet) {
     aLineLayout.RemoveBulletFrame(mBullet);

layout/html/base/src/nsLineBox.h

@@ -335,7 +335,10 @@ public:
   void AppendFloaters(nsFloaterCacheFreeList& aFreeList);
   PRBool RemoveFloater(nsIFrame* aFrame);
 
-  // Combined area
+  // Combined area is the area of the line that should influence the
+  // overflow area of its parent block.  The combined area should be
+  // used for painting-related things, but should never be used for
+  // layout (except for handling of 'overflow').
   void SetCombinedArea(const nsRect& aCombinedArea);
   void GetCombinedArea(nsRect* aResult);
   PRBool CombinedAreaIntersects(const nsRect& aDamageRect) {