Handle auto-positioned out-of-flow objects inside multicol containers correctly.

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

Index: third_party/WebKit/Source/core/layout/LayoutFlowThread.cpp
diff --git a/third_party/WebKit/Source/core/layout/LayoutFlowThread.cpp b/third_party/WebKit/Source/core/layout/LayoutFlowThread.cpp
index 5eae393e2aa636d4e15d5605d726220a4a2fb9e6..25708635bf75c2fd0d93779733c619af89100e86 100644
--- a/third_party/WebKit/Source/core/layout/LayoutFlowThread.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutFlowThread.cpp
@@ -187,6 +187,20 @@ LayoutRect LayoutFlowThread::fragmentsBoundingBox(const LayoutRect& layerBoundin
     return result;
 }
 
+void LayoutFlowThread::flowThreadToVisualLogicalPosition(LayoutUnit& blockPosition, LayoutUnit& inlinePosition)
+{
+    LayoutPoint position(inlinePosition, blockPosition);
+    if (!isHorizontalWritingMode())
+        position = position.transposedPoint();
+    position = flipForWritingMode(position);

[eae, 2016/08/16 18:23:45]

Instead of:

position = flipForWritingMode(position);
position.move(columnOffset(position));
position = flipForWritingMode(position);

why not do
position.move(columnOffset(flipForWritingMode(position)));
? or would that not have the same effect? The repeated updates of position makes
this code pretty hard to follow.

[mstensho (USE GERRIT), 2016/08/16 18:55:27]

columnOffset() works on physical coordinates, while
flowThreadToVisualLogicalPosition() and its callers are purely logical. So we
have to flip back and forth. I'll add some comments instead. See if that works
better.

+    position.move(columnOffset(position));
+    position = flipForWritingMode(position);
+    if (!isHorizontalWritingMode())
+        position = position.transposedPoint();
+    blockPosition = position.y();
+    inlinePosition = position.x();
+}
+
 void LayoutFlowThread::MultiColumnSetSearchAdapter::collectIfNeeded(const MultiColumnSetInterval& interval)
 {
     if (m_result)