[layoutng] Make sure to update m_isSelfCollapsing after ng layout

This will otherwise cause assertion failures on many pages.

We could also compute this in ng code during margin collapsing and just set it
on the old object, but I'm not sure that would be worth it.

This and https://codereview.chromium.org/2337763005/ fixes most (but not all)
of the assertion failures during legacy/ng interop.

R=ikilpatrick@chromium.org,eae@chromium.org,glebl@chromium.org
BUG=635619

Review-Url: https://codereview.chromium.org/2340113003
Cr-Commit-Position: refs/heads/master@{#418703}

third_party/WebKit/Source/core/layout/LayoutBlockFlow.cpp

@@ -412,7 +412,7 @@ void LayoutBlockFlow::layoutBlock(bool relayoutChildren)
         positionDialog();
 
     clearNeedsLayout();
-    m_isSelfCollapsing = checkIfIsSelfCollapsingBlock();
+    updateIsSelfCollapsing();
 }
 
 DISABLE_CFI_PERF

third_party/WebKit/Source/core/layout/LayoutBlockFlow.h

@@ -301,6 +301,10 @@ public:
     bool hasOverhangingFloats() const { return parent() && containsFloats() && lowestFloatLogicalBottom() > logicalHeight(); }
     bool isOverhangingFloat(const FloatingObject& floatObject) const { return logicalBottomForFloat(floatObject) > logicalHeight(); }
 
+    // This function is only public so we can call it from NGBox while we're
+    // still working on LayoutNG.
+    void updateIsSelfCollapsing() { m_isSelfCollapsing = checkIfIsSelfCollapsingBlock(); }
+
 #ifndef NDEBUG
     void showLineTreeAndMark(const InlineBox* = nullptr, const char* = nullptr, const InlineBox* = nullptr, const char* = nullptr, const LayoutObject* = nullptr) const;
 #endif

third_party/WebKit/Source/core/layout/ng/ng_box.cc

@@ -4,6 +4,7 @@
 
 #include "core/layout/ng/ng_box.h"
 
+#include "core/layout/LayoutBlockFlow.h"
 #include "core/layout/ng/layout_ng_block_flow.h"
 #include "core/layout/ng/ng_block_layout_algorithm.h"
 #include "core/layout/ng/ng_constraint_space.h"
@@ -63,6 +64,9 @@ bool NGBox::Layout(const NGConstraintSpace* constraint_space,
       if (layout_box_->isLayoutBlock())
         toLayoutBlock(layout_box_)->layoutPositionedObjects(true);
       layout_box_->clearNeedsLayout();
+      if (layout_box_->isLayoutBlockFlow()) {
+        toLayoutBlockFlow(layout_box_)->updateIsSelfCollapsing();
+      }
     }
   } else {
     DCHECK(layout_box_);