Untangle multicol coordinate space conversion from offsetFromContainer().

third_party/WebKit/Source/core/editing/CaretBase.cpp

Index: third_party/WebKit/Source/core/editing/CaretBase.cpp
diff --git a/third_party/WebKit/Source/core/editing/CaretBase.cpp b/third_party/WebKit/Source/core/editing/CaretBase.cpp
index c448ac207b47e6b33ec11a3e729be030a6052e9c..cbf557976a0b009a6a7928e2eed1d1cbead4d09a 100644
--- a/third_party/WebKit/Source/core/editing/CaretBase.cpp
+++ b/third_party/WebKit/Source/core/editing/CaretBase.cpp
@@ -82,7 +82,13 @@ static void mapCaretRectToCaretPainter(LayoutItem caretLayoutItem, LayoutBlockIt
             unrooted = true;
             break;
         }
-        caretRect.move(caretLayoutItem.offsetFromContainer(containerItem, caretRect.location()));
+        caretRect.move(caretLayoutItem.offsetFromContainer(containerItem));
+
+        // TODO(mstensho): Fix crbug.com/596070 and get rid of this flowthread/multicol thing
+        // here. It was added to keep the same behavior as before flowthread-to-visual coordinate
+        // space conversion was moved out from offsetFromContainer() to mapLocalToAncestor().
+        caretRect.move(containerItem.columnOffset(caretRect.location()));
+
         caretLayoutItem = containerItem;
     }