Add clean layout DCHECK to mostBackwardCaretPosition()

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

Index: third_party/WebKit/Source/core/editing/VisibleSelection.cpp
diff --git a/third_party/WebKit/Source/core/editing/VisibleSelection.cpp b/third_party/WebKit/Source/core/editing/VisibleSelection.cpp
index 8d89792653f41418faea5f8a3e9a1dd4f115a4f3..575eb84fe4e258a1d999f714cd55bac82dee37f7 100644
--- a/third_party/WebKit/Source/core/editing/VisibleSelection.cpp
+++ b/third_party/WebKit/Source/core/editing/VisibleSelection.cpp
@@ -194,7 +194,7 @@ VisibleSelectionTemplate<Strategy>::toNormalizedEphemeralRange() const {
   // in the course of running edit commands which modify the DOM.
   // Failing to ensure this can result in equivalentXXXPosition calls returning
   // incorrect results.
-  DCHECK(!m_start.document()->needsLayoutTreeUpdate());
+  DCHECK(!needsLayoutTreeUpdate(m_start)) << *this;
 
   if (isCaret()) {
     // If the selection is a caret, move the range start upstream. This