*** FOR PROTOTYPE PURPOSES ONLY! NOT INTENDED FOR COMMIT! ***

Source/core/rendering/RenderBlock.cpp

Index: Source/core/rendering/RenderBlock.cpp
diff --git a/Source/core/rendering/RenderBlock.cpp b/Source/core/rendering/RenderBlock.cpp
index 6eec95fcc9a3d75a9217179e9ec19b42302478a8..06cb03d2abb7145a12991c8ee5d2b2cfda76fc9a 100644
--- a/Source/core/rendering/RenderBlock.cpp
+++ b/Source/core/rendering/RenderBlock.cpp
@@ -1305,6 +1305,34 @@ void RenderBlock::layout()
     invalidateBackgroundObscurationStatus();
 }
 
+void RenderBlock::preLayout()
+{
+    OverflowEventDispatcher dispatcher(this);
+    LayoutRectRecorder recorder(*this);

[eseidel, 2014/02/15 00:37:18]

This won't work, it will expect that layout is done when its destructor is
called.

One of the unfortunate effects of splitting layout() into halves is that all of
our existing RAIIs (like this one) will be confused.  We'll need to instead push
these RAIIs on a stack?

[atreat, 2014/02/18 16:03:57]

Yes, this one I missed and we'll need a stack.  More on that in another comment.

[dsinclair, 2014/02/18 16:07:06]

LayoutRectRecorder should be fine, you just have to make sure you create it in
both the pre and post layout. It's already designed that if you call it multiple
times it will set the oldRepaintRect size and won't over-write it, but it will
over-write newRepaintRect when it's created a second time. So, you shouldn't
need a special stack of them.

+
+    // Update our first letter info now.
+    updateFirstLetter();
+
+    // Table cells call layoutBlock directly, so don't add any logic here.  Put code into
+    // layoutBlock().
+    preLayoutBlock(false, false);
+}
+
+void RenderBlock::postLayout()
+{
+    postLayoutBlock();
+
+    if (frameView()->partialLayout().isStopping())
+        return;
+
+    // It's safe to check for control clip here, since controls can never be table cells.
+    // If we have a lightweight clip, there can never be any overflow from children.
+    if (hasControlClip() && m_overflow)
+        clearLayoutOverflow();
+
+    invalidateBackgroundObscurationStatus();
+}
+
 bool RenderBlock::updateImageLoadingPriorities()
 {
     Vector<ImageResource*> images;
@@ -1515,6 +1543,18 @@ void RenderBlock::layoutBlock(bool)
     clearNeedsLayout();
 }
 
+void RenderBlock::preLayoutBlock(bool, bool)
+{
+    ASSERT_NOT_REACHED();
+    clearNeedsLayout();
+}
+
+bool RenderBlock::postLayoutBlock()
+{
+    ASSERT_NOT_REACHED();
+    return false;
+}
+
 void RenderBlock::addOverflowFromChildren()
 {
     if (!hasColumns()) {