Introduce isRenderedCharacter(Position) function

Source/core/editing/commands/InsertParagraphSeparatorCommand.cpp

Index: Source/core/editing/commands/InsertParagraphSeparatorCommand.cpp
diff --git a/Source/core/editing/commands/InsertParagraphSeparatorCommand.cpp b/Source/core/editing/commands/InsertParagraphSeparatorCommand.cpp
index d914179bc8615d06365059870b9678122542cc98..4032caa787348beb8f575961b56112db753f929b 100644
--- a/Source/core/editing/commands/InsertParagraphSeparatorCommand.cpp
+++ b/Source/core/editing/commands/InsertParagraphSeparatorCommand.cpp
@@ -417,7 +417,9 @@ void InsertParagraphSeparatorCommand::doApply()
     // Handle whitespace that occurs after the split
     if (positionAfterSplit.isNotNull()) {
         document().updateLayoutIgnorePendingStylesheets();
-        if (!positionAfterSplit.isRenderedCharacter()) {
+        // TODO(yosin) |isRenderedCharacter()| should be removed, and we should
+        // use |VisiblePosition::characterAfter()|.
+        if (!isRenderedCharacter(positionAfterSplit)) {
             // Clear out all whitespace and insert one non-breaking space
             ASSERT(!positionAfterSplit.computeContainerNode()->layoutObject() || positionAfterSplit.computeContainerNode()->layoutObject()->style()->collapseWhiteSpace());
             deleteInsignificantTextDownstream(positionAfterSplit);