Bug 899896 - Avoid null checking of some box layout factory functions. r=dbaron

layout/xul/base/src/nsListBoxBodyFrame.cpp

@@ -1474,10 +1474,6 @@ nsIFrame*
 NS_NewListBoxBodyFrame(nsIPresShell* aPresShell, nsStyleContext* aContext)
 {
   nsCOMPtr<nsBoxLayout> layout = NS_NewListBoxLayout();
-  if (!layout) {
-    return nullptr;
-  }
-
   return new (aPresShell) nsListBoxBodyFrame(aPresShell, aContext, layout);
 }
 

layout/xul/grid/nsGridRowGroupFrame.cpp

@@ -23,10 +23,6 @@ NS_NewGridRowGroupFrame(nsIPresShell* aPresShell,
                         nsStyleContext* aContext)
 {
   nsCOMPtr<nsBoxLayout> layout = NS_NewGridRowGroupLayout();
-  if (!layout) {
-    return nullptr;
-  }
-
   return new (aPresShell) nsGridRowGroupFrame(aPresShell, aContext, layout);
 }
 

layout/xul/grid/nsGridRowLeafFrame.cpp

@@ -23,10 +23,6 @@ NS_NewGridRowLeafFrame(nsIPresShell* aPresShell,
                        nsStyleContext* aContext)
 {
   nsCOMPtr<nsBoxLayout> layout = NS_NewGridRowLeafLayout();
-  if (!layout) {
-    return nullptr;
-  }
-  
   return new (aPresShell) nsGridRowLeafFrame(aPresShell, aContext, false,
                                              layout);
 }