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..d06023af371e082ad2d3dbd894a681681fe4e2e1 100644
--- a/third_party/WebKit/Source/core/editing/CaretBase.cpp
+++ b/third_party/WebKit/Source/core/editing/CaretBase.cpp
@@ -82,7 +82,15 @@ 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().
+        LayoutObject* containerObject = (LayoutObject*)containerItem;

[mstensho (USE GERRIT), 2016/03/18 20:51:40]

Pretty sure I'm violating the API encapsulation like a real h4x0r here. :) The
other option would be to add a temporary method to the LayoutItem API, but that
seems silly, since the patch that removes this code is more or less ready to be
filed already.

[leviw_travelin_and_unemployed, 2016/03/18 22:27:02]

Really you should be adding that method to the API here. It's not so bad :)

[mstensho (USE GERRIT), 2016/03/18 22:45:23]

Done.

+        if (containerObject->isLayoutFlowThread())
+            caretRect.move(containerObject->columnOffset(caretRect.location()));
+
         caretLayoutItem = containerItem;
     }