Convert USERSELECT_ALL to a runtime enabled feature.

Source/core/editing/htmlediting.cpp

Index: Source/core/editing/htmlediting.cpp
diff --git a/Source/core/editing/htmlediting.cpp b/Source/core/editing/htmlediting.cpp
index b4b945928a199c3acde95cf5b9dceebe9e5939a4..72bf50d73ec44295a60cb3819431b263c0e85241 100644
--- a/Source/core/editing/htmlediting.cpp
+++ b/Source/core/editing/htmlediting.cpp
@@ -101,6 +101,11 @@ int comparePositions(const Position& a, const Position& b)
     return result ? result : bias;
 }
 
+int comparePositions(const PositionWithAffinity& a, const PositionWithAffinity& b)
+{
+    return comparePositions(a.position(), b.position());
+}
+
 int comparePositions(const VisiblePosition& a, const VisiblePosition& b)
 {
     return comparePositions(a.deepEquivalent(), b.deepEquivalent());