Begin tracking why layout is invalidated

Source/core/layout/LayoutMultiColumnFlowThread.cpp

Index: Source/core/layout/LayoutMultiColumnFlowThread.cpp
diff --git a/Source/core/layout/LayoutMultiColumnFlowThread.cpp b/Source/core/layout/LayoutMultiColumnFlowThread.cpp
index 5febbf5582babd2f2eef97e9fd8cbbd6a89127bc..f4c35516f23c8ae7b3d36284bd93564d9d478d25 100644
--- a/Source/core/layout/LayoutMultiColumnFlowThread.cpp
+++ b/Source/core/layout/LayoutMultiColumnFlowThread.cpp
@@ -472,7 +472,7 @@ void LayoutMultiColumnFlowThread::flowThreadDescendantWasInserted(LayoutObject*
                         // a new spanner placeholder between them.
                         setToSplit = findSetRendering(previousRenderer);
                         ASSERT(setToSplit == findSetRendering(nextRenderer));
-                        setToSplit->setNeedsLayoutAndFullPaintInvalidation();
+                        setToSplit->setNeedsLayoutAndFullPaintInvalidation(LayoutInvalidationReason::ColumnsChanged);
                         insertBefore = setToSplit->nextSiblingMultiColumnBox();
                         // We've found out which set that needs to be split. Now proceed to
                         // inserting the spanner placeholder, and then insert a second column set.
@@ -531,7 +531,7 @@ void LayoutMultiColumnFlowThread::flowThreadDescendantWillBeRemoved(LayoutObject
                 && previousColumnBox && previousColumnBox->isLayoutMultiColumnSet()) {
                 // Need to merge two column sets.
                 nextColumnBox->destroy();
-                previousColumnBox->setNeedsLayout();
+                previousColumnBox->setNeedsLayout(LayoutInvalidationReason::Unknown);

[esprehn, 2015/03/23 20:19:44]

ColumnsChanged

                 invalidateRegions();
             }
         }