Improving direction-based selection strategy.

Source/core/editing/VisibleSelection.cpp

Index: Source/core/editing/VisibleSelection.cpp
diff --git a/Source/core/editing/VisibleSelection.cpp b/Source/core/editing/VisibleSelection.cpp
index 432cfc52e0e0a3b2e67fc6ffb3faa5f68e2ef42a..25619dfcc13ee853d29050ea5fb1bc107d310788 100644
--- a/Source/core/editing/VisibleSelection.cpp
+++ b/Source/core/editing/VisibleSelection.cpp
@@ -593,6 +593,23 @@ void VisibleSelection::setWithoutValidation(const Position& base, const Position
     didChange();
 }
 
+void VisibleSelection::setWithoutValidation(const Position& base, const Position& extent, const Position& start, const Position& end)
+{
+    ASSERT(!base.isNull());
+    ASSERT(!extent.isNull());
+    ASSERT(!start.isNull());
+    ASSERT(!end.isNull());
+    ASSERT(m_affinity == DOWNSTREAM);
+    ASSERT(comparePositions(start, end) <= 0);
+    m_base = base;
+    m_extent = extent;
+    m_baseIsFirst = comparePositions(base, extent) <= 0;
+    m_start = start;
+    m_end = end;
+    m_selectionType = base == extent ? CaretSelection : RangeSelection;
+    didChange();
+}
+
 static Position adjustPositionForEnd(const Position& currentPosition, Node* startContainerNode)
 {
     TreeScope& treeScope = startContainerNode->treeScope();