Introduce VisiblePosition::isValid

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 8389684c3bb0a35ded794d25debfa5fae2dbaedd..09d07a49bf76a65a8a52f2de2be4c5b7afea0d12 100644
--- a/third_party/WebKit/Source/core/editing/VisibleUnits.cpp
+++ b/third_party/WebKit/Source/core/editing/VisibleUnits.cpp
@@ -1337,14 +1337,14 @@ static inline LayoutPoint absoluteLineDirectionPointToLocalPointInBlock(RootInli
 
 VisiblePosition previousLinePosition(const VisiblePosition& visiblePosition, LayoutUnit lineDirectionPoint, EditableType editableType)
 {
+    DCHECK(visiblePosition.isValid());
+
     Position p = visiblePosition.deepEquivalent();
     Node* node = p.anchorNode();
 
     if (!node)
         return VisiblePosition();
 
-    DCHECK(!node->document().needsLayoutTreeUpdate());
-
     LayoutObject* layoutObject = node->layoutObject();
     if (!layoutObject)
         return VisiblePosition();
@@ -1390,14 +1390,14 @@ VisiblePosition previousLinePosition(const VisiblePosition& visiblePosition, Lay
 
 VisiblePosition nextLinePosition(const VisiblePosition& visiblePosition, LayoutUnit lineDirectionPoint, EditableType editableType)
 {
+    DCHECK(visiblePosition.isValid());
+
     Position p = visiblePosition.deepEquivalent();
     Node* node = p.anchorNode();
 
     if (!node)
         return VisiblePosition();
 
-    DCHECK(!node->document().needsLayoutTreeUpdate());
-
     LayoutObject* layoutObject = node->layoutObject();
     if (!layoutObject)
         return VisiblePosition();