Complete layout even if a block needs relayout due to widows or column balancing.

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

Index: third_party/WebKit/Source/core/layout/LayoutBlockFlow.cpp
diff --git a/third_party/WebKit/Source/core/layout/LayoutBlockFlow.cpp b/third_party/WebKit/Source/core/layout/LayoutBlockFlow.cpp
index cb24181eb5e898624e4af9336fe065fd549b2118..7e6fdb4f294712cb5e131e1a462442d7a1dc7fd6 100644
--- a/third_party/WebKit/Source/core/layout/LayoutBlockFlow.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutBlockFlow.cpp
@@ -403,9 +403,21 @@ void LayoutBlockFlow::layoutBlock(bool relayoutChildren) {
 
   // Multiple passes might be required for column based layout.
   // The number of passes could be as high as the number of columns.
-  bool done = false;
-  while (!done)
-    done = layoutBlockFlow(relayoutChildren, layoutScope);
+  LayoutMultiColumnFlowThread* flowThread = multiColumnFlowThread();
+  do {
+    layoutBlockFlow(relayoutChildren, layoutScope);
+
+    if (flowThread && flowThread->columnHeightsChanged()) {
+      setChildNeedsLayout(MarkOnlyThis);
+      continue;
+    }
+
+    if (shouldBreakAtLineToAvoidWidow()) {
+      setEverHadLayout();
+      continue;
+    }
+    break;
+  } while (true);
 
   updateLayerTransformAfterLayout();
 
@@ -462,7 +474,7 @@ void LayoutBlockFlow::resetLayout() {
 }
 
 DISABLE_CFI_PERF
-inline bool LayoutBlockFlow::layoutBlockFlow(bool relayoutChildren,
+inline void LayoutBlockFlow::layoutBlockFlow(bool relayoutChildren,
                                              SubtreeLayoutScope& layoutScope) {
   LayoutUnit oldLeft = logicalLeft();
   bool logicalWidthChanged = updateLogicalWidthAndColumnWidth();
@@ -503,7 +515,8 @@ inline bool LayoutBlockFlow::layoutBlockFlow(bool relayoutChildren,
     // potential infinite loop, run layout again with auto scrollbars frozen in
     // their current state.
     PaintLayerScrollableArea::FreezeScrollbarsScope freezeScrollbars;
-    return layoutBlockFlow(relayoutChildren, layoutScope);
+    layoutBlockFlow(relayoutChildren, layoutScope);

[szager1, 2016/12/01 17:43:24]

Please add:

DCHECK(preferredLogicalWidthsWereDirty || !preferredLogicalWidthsDirty());

[mstensho (USE GERRIT), 2016/12/01 18:11:47]

We can be pretty sure that !preferredLogicalWidthsWereDirty at this point. So I
suppose it's sufficient to DCHECK(!preferredLogicalWidthsDirty()), right?

[mstensho (USE GERRIT), 2016/12/01 19:15:34]

Hmm... scrollbars/overflow-auto-infinite-loop.html crashes then. Maybe deal with
this separately?

[szager1, 2016/12/01 20:30:12]

There's a reason why I added preferredLogicalWidthsWereDirty, rather than just
checking preferredLogicalWidthsDirty() after layoutBlockChildren.  There are
some legitimate cases where this code runs while preferred widths are dirty (I
don't remember exactly why).  So, we only want to flag the case where preferred
widths were clean and became dirty.

[mstensho (USE GERRIT), 2016/12/01 20:36:10]

But we only get here if preferredLogicalWidthsBecameDirty, i.e. if
!preferredLogicalWidthsWereDirty && preferredLogicalWidthsDirty(). So I don't
understand how preferredLogicalWidthsWereDirty can be true here.

(preferred widths are dirty and remain dirty on any object that doesn't need its
min/max widths calculated, but maybe you had something more specific in mind)

+    return;
   }
 
   // Expand our intrinsic height to encompass floats.
@@ -511,18 +524,6 @@ inline bool LayoutBlockFlow::layoutBlockFlow(bool relayoutChildren,
       createsNewFormattingContext())
     setLogicalHeight(lowestFloatLogicalBottom() + afterEdge);
 
-  if (LayoutMultiColumnFlowThread* flowThread = multiColumnFlowThread()) {
-    if (flowThread->columnHeightsChanged()) {
-      setChildNeedsLayout(MarkOnlyThis);
-      return false;
-    }
-  }
-
-  if (shouldBreakAtLineToAvoidWidow()) {
-    setEverHadLayout();
-    return false;
-  }
-
   // Remember the automatic logical height we got from laying out the children.
   LayoutUnit unconstrainedHeight = logicalHeight();
   LayoutUnit unconstrainedClientAfterEdge = clientLogicalBottom();
@@ -546,7 +547,6 @@ inline bool LayoutBlockFlow::layoutBlockFlow(bool relayoutChildren,
   computeOverflow(unconstrainedClientAfterEdge);
 
   m_descendantsWithFloatsMarkedForLayout = false;
-  return true;
 }
 
 void LayoutBlockFlow::addOverhangingFloatsFromChildren(