Begin tracking why layout is invalidated

Source/core/layout/LayoutMultiColumnFlowThread.cpp

 /*
  * Copyright (C) 2012 Apple Inc.  All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 466 matching lines @@
                         insertBefore = firstMultiColumnBox();
                     } else if (LayoutMultiColumnSpannerPlaceholder* previousPlaceholder = containingColumnSpannerPlaceholder(previousRenderer)) {
                         // Before us is another spanner. We belong right after it then.
                         insertBefore = previousPlaceholder->nextSiblingMultiColumnBox();
                     } else {
                         // We're inside regular column content with both feet. Find out which column
                         // set this is. It needs to be split it into two sets, so that we can insert
                         // 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.
                     }
                 }
                 ASSERT(setToSplit || insertBefore);
             }
             createAndInsertSpannerPlaceholder(toLayoutBox(renderer), insertBefore);
             if (setToSplit)
                 createAndInsertMultiColumnSet(insertBefore);
@@ skipping 38 matching lines @@
             next = renderer->nextInPreOrder(descendant);
             continue;
         }
         next = renderer->nextInPreOrderAfterChildren(descendant); // It's a spanner. Its children are of no interest to us.
         if (LayoutBox* nextColumnBox = placeholder->nextSiblingMultiColumnBox()) {
             LayoutBox* previousColumnBox = placeholder->previousSiblingMultiColumnBox();
             if (nextColumnBox && nextColumnBox->isLayoutMultiColumnSet()
                 && previousColumnBox && previousColumnBox->isLayoutMultiColumnSet()) {
                 // Need to merge two column sets.
                 nextColumnBox->destroy();
-                previousColumnBox->setNeedsLayout();
+                previousColumnBox->setNeedsLayout(LayoutInvalidationReason::ColumnsChanged);
                 invalidateRegions();
             }
         }
         placeholder->destroy();
     }
     if (hadContainingPlaceholder)
         return; // We're only removing a spanner (or something inside one), which means that no column content will be removed.
 
     // Column content will be removed. Does this mean that we should destroy a column set?
     LayoutMultiColumnSpannerPlaceholder* adjacentPreviousSpannerPlaceholder = 0;
@@ skipping 118 matching lines @@
 }
 
 bool LayoutMultiColumnFlowThread::isPageLogicalHeightKnown() const
 {
     if (LayoutMultiColumnSet* columnSet = lastMultiColumnSet())
         return columnSet->pageLogicalHeight();
     return false;
 }
 
 }