[Experiment] DCHECK clean layout tree in mostForward/BackwardCaretPosition

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

Index: third_party/WebKit/Source/core/editing/VisibleUnits.cpp
diff --git a/third_party/WebKit/Source/core/editing/VisibleUnits.cpp b/third_party/WebKit/Source/core/editing/VisibleUnits.cpp
index 02aa28ad9febd56dfd8818de2bec1b76af3997b5..1c7bc8bf2184903859299416aeaaee20b540c408 100644
--- a/third_party/WebKit/Source/core/editing/VisibleUnits.cpp
+++ b/third_party/WebKit/Source/core/editing/VisibleUnits.cpp
@@ -2821,6 +2821,8 @@ static PositionTemplate<Strategy> mostBackwardCaretPosition(
   if (!startNode)
     return PositionTemplate<Strategy>();
 
+  if (!startNode->document().frame()->selection().inUpdateSelectionIfNeeded())
+    DCHECK(!startNode->document().needsLayoutTreeUpdate());
   // iterate backward from there, looking for a qualified position
   Node* boundary = enclosingVisualBoundary<Strategy>(startNode);
   // FIXME: PositionIterator should respect Before and After positions.
@@ -2995,6 +2997,8 @@ PositionTemplate<Strategy> mostForwardCaretPosition(
   if (!startNode)
     return PositionTemplate<Strategy>();
 
+  if (!startNode->document().frame()->selection().inUpdateSelectionIfNeeded())
+    DCHECK(!startNode->document().needsLayoutTreeUpdate());
   // iterate forward from there, looking for a qualified position
   Node* boundary = enclosingVisualBoundary<Strategy>(startNode);
   // FIXME: PositionIterator should respect Before and After positions.