RenderBlock::isSelfCollapsingBlock() should early exit on a relayout boundary

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 bffaf6158c322e099bcaf57f4dab15055e777396..55756705e51df0fba7e67f74226ad66b75eb0ed5 100644
--- a/Source/core/rendering/RenderBlock.cpp
+++ b/Source/core/rendering/RenderBlock.cpp
@@ -1178,11 +1178,6 @@ void RenderBlock::removeChild(RenderObject* oldChild)
 
 bool RenderBlock::isSelfCollapsingBlock() const
 {
-    // Placeholder elements are not laid out until the dimensions of their parent text control are known, so they
-    // don't get layout until their parent has had layout - this is unique in the layout tree and means
-    // when we call isSelfCollapsingBlock on them we find that they still need layout.
-    ASSERT(!needsLayout() || (node() && node()->isElementNode() && toElement(node())->shadowPseudoId() == "-webkit-input-placeholder"));
-
     // We are not self-collapsing if we
     // (a) have a non-zero height according to layout (an optimization to avoid wasting time)
     // (b) are a table,
@@ -1191,9 +1186,18 @@ bool RenderBlock::isSelfCollapsingBlock() const
     // (e) have specified that one of our margins can't collapse using a CSS extension
     // (f) establish a new block formatting context.
 
+    // The early exit must be done before we check for clean layout.
+    // We should be able to give a quick answer if the box is a relayout boundary.
+    // Being a relayout boundary implies a block formatting context, and also

[ojan, 2014/04/24 17:22:09]

This comment is a little confusing. It talks about relayout boundaries, but the
code is only checking block formatting context. 

+    // our internal layout shouldn't affect our container in any way.
     if (createsBlockFormattingContext())
         return false;
 
+    // Placeholder elements are not laid out until the dimensions of their parent text control are known, so they
+    // don't get layout until their parent has had layout - this is unique in the layout tree and means
+    // when we call isSelfCollapsingBlock on them we find that they still need layout.
+    ASSERT(!needsLayout() || (node() && node()->isElementNode() && toElement(node())->shadowPseudoId() == "-webkit-input-placeholder"));
+
     if (logicalHeight() > 0
         || isTable() || borderAndPaddingLogicalHeight()
         || style()->logicalMinHeight().isPositive()