Move character{After,Before}() for VisiblePosition to VisibleUnits.cpp

Source/core/editing/VisibleUnits.cpp

Index: Source/core/editing/VisibleUnits.cpp
diff --git a/Source/core/editing/VisibleUnits.cpp b/Source/core/editing/VisibleUnits.cpp
index 65353feb5cc9d42d40ab4bb5f92ab93931693fe0..4e63a99c2592c7c39ff47f8a9a83f44093885691 100644
--- a/Source/core/editing/VisibleUnits.cpp
+++ b/Source/core/editing/VisibleUnits.cpp
@@ -2359,6 +2359,31 @@ static VisiblePosition skipToEndOfEditingBoundary(const VisiblePosition& pos, co
     return firstEditableVisiblePositionAfterPositionInRoot(pos.deepEquivalent(), highestRoot);
 }
 
+UChar32 characterAfter(const VisiblePosition& visiblePosition)
+{
+    // We canonicalize to the first of two equivalent candidates, but the second
+    // of the two candidates is the one that will be inside the text node
+    // containing the character after this visible position.
+    Position pos = mostForwardCaretPosition(visiblePosition.deepEquivalent());
+    if (!pos.isOffsetInAnchor())
+        return 0;
+    Node* containerNode = pos.computeContainerNode();
+    if (!containerNode || !containerNode->isTextNode())
+        return 0;
+    unsigned offset = static_cast<unsigned>(pos.offsetInContainerNode());
+    Text* textNode = toText(containerNode);
+    unsigned length = textNode->length();
+    if (offset >= length)
+        return 0;
+
+    return textNode->data().characterStartingAt(offset);
+}
+
+UChar32 characterBefore(const VisiblePosition& visiblePosition)
+{
+    return characterAfter(previousPositionOf(visiblePosition));
+}
+
 VisiblePosition nextPositionOf(const VisiblePosition& visiblePosition, EditingBoundaryCrossingRule rule)
 {
     VisiblePosition next(nextVisuallyDistinctCandidate(visiblePosition.deepEquivalent()), visiblePosition.affinity());