Adjust column rows' height better for their offset in the multicol container.

third_party/WebKit/Source/core/layout/MultiColumnFragmentainerGroup.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/MultiColumnFragmentainerGroup.h"
 
 #include "core/layout/ColumnBalancer.h"
 #include "core/layout/FragmentationContext.h"
 #include "core/layout/LayoutMultiColumnSet.h"
 
@@ skipping 274 matching lines @@
     unsigned count = (flowThreadPortionHeight / m_columnHeight).floor();
     // flowThreadPortionHeight may be saturated, so detect the remainder manually.
     if (count * m_columnHeight < flowThreadPortionHeight)
         count++;
     ASSERT(count >= 1);
     return count;
 }
 
 LayoutUnit MultiColumnFragmentainerGroup::heightAdjustedForRowOffset(LayoutUnit height) const
 {
-    // Adjust for the top offset within the content box of the multicol container (containing
-    // block), unless we're in the first set. We know that the top offset for the first set will be
-    // zero, but if the multicol container has non-zero top border or padding, the set's top offset
-    // (initially being 0 and relative to the border box) will be negative until it has been laid
-    // out. Had we used this bogus offset, we would calculate the wrong height, and risk performing
-    // a wasted layout iteration. Of course all other sets (if any) have this problem in the first
-    // layout pass too, but there's really nothing we can do there until the flow thread has been
-    // laid out anyway.
-    if (m_columnSet.previousSiblingMultiColumnSet()) {
-        LayoutBlockFlow* multicolBlock = m_columnSet.multiColumnBlockFlow();
-        LayoutUnit contentLogicalTop = m_columnSet.logicalTop() - multicolBlock->borderAndPaddingBefore();
-        height -= contentLogicalTop;
-    }
-    height -= logicalTop();
-    return max(height, LayoutUnit(1)); // Let's avoid zero height, as that would probably cause an infinite amount of columns to be created.
+    // Let's avoid zero height, as that would cause an infinite amount of columns to be created.

[leviw_travelin_and_unemployed, 2016/01/26 23:00:29]

Where's the fun in that?

If we can just sell the columns for $0.01 we'll be RICH! Think of all the spam,
sausage, lobster, egg, bread, and beer we could buy!

[mstensho (USE GERRIT), 2016/01/27 09:51:45]

I can do that in a follow-up patch. You're right. This can be monetized! Surely
there's a market for all the super-short columns that we don't need.

+    return std::max(height - logicalTop() - m_columnSet.logicalTopFromMulticolContentEdge(), LayoutUnit(1));
 }
 
 LayoutUnit MultiColumnFragmentainerGroup::calculateMaxColumnHeight() const
 {
     LayoutBlockFlow* multicolBlock = m_columnSet.multiColumnBlockFlow();
     const ComputedStyle& multicolStyle = multicolBlock->styleRef();
     LayoutMultiColumnFlowThread* flowThread = m_columnSet.multiColumnFlowThread();
     LayoutUnit availableHeight = flowThread->columnHeightAvailable();
     LayoutUnit maxColumnHeight = availableHeight ? availableHeight : LayoutUnit::max();
     if (!multicolStyle.logicalMaxHeight().isMaxSizeNone()) {
@@ skipping 232 matching lines @@
     append(MultiColumnFragmentainerGroup(m_columnSet));
     return last();
 }
 
 void MultiColumnFragmentainerGroupList::deleteExtraGroups()
 {
     shrink(1);
 }
 
 } // namespace blink