ColumnBalancer: Count line box overflow as space shortage.

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

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/layout/ColumnBalancer.h"
 
 #include "core/layout/LayoutMultiColumnFlowThread.h"
 #include "core/layout/LayoutMultiColumnSet.h"
 #include "core/layout/api/LineLayoutBlockFlow.h"
 
@@ skipping 307 matching lines @@
         // that block. We want to record the distance from the top of the column to the bottom of
         // this box as space shortage.
         LayoutUnit logicalOffsetFromCurrentColumn = lineTopInFlowThread - group().columnLogicalTopForOffset(lineTopInFlowThread);
         recordSpaceShortage(logicalOffsetFromCurrentColumn + lineHeight - m_pendingStrut);
         m_pendingStrut = LayoutUnit::min();
         return;
     }
     ASSERT(isFirstAfterBreak(lineTopInFlowThread) || !line.paginationStrut() || !isLogicalTopWithinBounds(lineTopInFlowThread - line.paginationStrut()));
     if (isFirstAfterBreak(lineTopInFlowThread))
         recordSpaceShortage(lineHeight - line.paginationStrut());
+
+    // Even if the line box itself fits fine inside a column, some content may overflow the line
+    // box bottom (due to restrictive line-height, for instance). We should check if some portion
+    // of said overflow ends up in the next column. That counts as space shortage.
+    LayoutUnit lineBottomWithOverflow = lineTopInFlowThread + line.lineBottom() - lineTop;
+    if (group().columnLogicalTopForOffset(lineTopInFlowThread) != group().columnLogicalTopForOffset(lineBottomWithOverflow)) {
+        LayoutUnit shortage = lineBottomWithOverflow - group().columnLogicalTopForOffset(lineBottomWithOverflow);
+        recordSpaceShortage(shortage);
+    }
 }
 
 } // namespace blink