1. Make scroll frames non-splittable.

2. Make a placeholder splittable only if the out-of-flow is.
3. If a float placeholder is not splittable then place it immediately
   instead of failing to reflow it because it can't be split.
b=337419 (Patch B) r+sr=roc

layout/base/nsCSSFrameConstructor.cpp

@@ -10984,6 +10984,13 @@ nsCSSFrameConstructor::CreateContinuingFrame(nsPresContext* aPresContext,
   nsIAtom* frameType = aFrame->GetType();
   nsIContent* content = aFrame->GetContent();
 
+#ifdef NS_DEBUG
+    nsSplittableType splitType;
+    aFrame->IsSplittable(splitType);
+    NS_ASSERTION(splitType != NS_FRAME_NOT_SPLITTABLE,
+                 "why CreateContinuingFrame for a non-splittable frame?");
+#endif
+  
   if (nsLayoutAtoms::textFrame == frameType) {
     newFrame = NS_NewContinuingTextFrame(shell, styleContext);
 

layout/generic/nsBlockReflowState.cpp

@@ -24,6 +24,7 @@
  *   Steve Clark <buster@netscape.com>
  *   Robert O'Callahan <roc+moz@cs.cmu.edu>
  *   L. David Baron <dbaron@dbaron.org>
+ *   Mats Palmgren <mats.palmgren@bredband.net>
  *
  * Alternatively, the contents of this file may be used under the terms of
  * either of the GNU General Public License Version 2 or later (the "GPL"),
@@ -656,9 +657,19 @@ nsBlockReflowState::AddFloat(nsLineLayout&       aLineLayout,
       // prevent the placeholders being torn down. We will destroy any
       // placeholders later if PlaceBelowCurrentLineFloats finds the
       // float is complete.
-      aReflowStatus = NS_FRAME_NOT_COMPLETE;
+      nsSplittableType splitType;
+      aPlaceholder->IsSplittable(splitType);
+      if (splitType == NS_FRAME_NOT_SPLITTABLE) {
+        placed = PR_FALSE;
+      }
+      else {
+        placed = PR_TRUE;
+        aReflowStatus = NS_FRAME_NOT_COMPLETE;
+      }
+    }
+    else {
+      placed = PR_TRUE;
     }
-    placed = PR_TRUE;
   }
   return placed;
 }

layout/generic/nsGfxScrollFrame.cpp

@@ -213,6 +213,12 @@ nsHTMLScrollFrame::RemoveFrame(nsIAtom*  aListName,
   return NS_OK;
 }
 
+NS_IMETHODIMP
+nsHTMLScrollFrame::IsSplittable(nsSplittableType& aIsSplittable) const
+{
+  aIsSplittable = NS_FRAME_NOT_SPLITTABLE;
+  return NS_OK;
+}
 
 PRIntn
 nsHTMLScrollFrame::GetSkipSides() const
@@ -1047,6 +1053,12 @@ nsXULScrollFrame::RemoveFrame(nsIAtom*        aListName,
   return rv;
 }
 
+NS_IMETHODIMP
+nsXULScrollFrame::IsSplittable(nsSplittableType& aIsSplittable) const
+{
+  aIsSplittable = NS_FRAME_NOT_SPLITTABLE;
+  return NS_OK;
+}
 
 NS_IMETHODIMP
 nsXULScrollFrame::GetPadding(nsMargin& aMargin)

layout/generic/nsGfxScrollFrame.h

@@ -277,6 +277,7 @@ public:
 
   virtual PRBool NeedsView() { return PR_TRUE; }
   virtual PRBool DoesClipChildren() { return PR_TRUE; }
+  NS_IMETHOD IsSplittable(nsSplittableType& aIsSplittable) const;
 
   virtual nsPoint GetPositionOfChildIgnoringScrolling(nsIFrame* aChild)
   { nsPoint pt = aChild->GetPosition();
@@ -424,6 +425,7 @@ public:
 
   virtual PRBool NeedsView() { return PR_TRUE; }
   virtual PRBool DoesClipChildren() { return PR_TRUE; }
+  NS_IMETHOD IsSplittable(nsSplittableType& aIsSplittable) const;
 
   virtual nsPoint GetPositionOfChildIgnoringScrolling(nsIFrame* aChild)
   { nsPoint pt = aChild->GetPosition();

layout/generic/nsPlaceholderFrame.cpp

@@ -92,6 +92,13 @@ nsPlaceholderFrame::Destroy()
   nsSplittableFrame::Destroy();
 }
 
+NS_IMETHODIMP
+nsPlaceholderFrame::IsSplittable(nsSplittableType& aIsSplittable) const
+{
+  NS_ASSERTION(mOutOfFlowFrame, "IsSplittable called at the wrong time");
+  return mOutOfFlowFrame->IsSplittable(aIsSplittable);
+}
+
 nsIAtom*
 nsPlaceholderFrame::GetType() const
 {

layout/generic/nsPlaceholderFrame.h

@@ -72,6 +72,7 @@ public:
                     nsReflowStatus& aStatus);
 
   virtual void Destroy();
+  NS_IMETHOD IsSplittable(nsSplittableType& aIsSplittable) const;
 
   // nsIFrame overrides
 #ifdef DEBUG