Keep the selection of the text field when changed by JS.

Source/core/editing/SelectionController.cpp

Index: Source/core/editing/SelectionController.cpp
diff --git a/Source/core/editing/SelectionController.cpp b/Source/core/editing/SelectionController.cpp
index 537e809b2414b2b0777f4e30a9eb21f3a858e83b..b000f175d4c699892e1ccb42205d836e6ccab4db 100644
--- a/Source/core/editing/SelectionController.cpp
+++ b/Source/core/editing/SelectionController.cpp
@@ -193,7 +193,7 @@ bool SelectionController::handleMousePressEventSingleClickAlgorithm(const MouseE
             granularity = selection().granularity();
             expandSelectionUsingGranularity(newSelection, selection().granularity());
         }
-    } else {
+    } else if (m_selectionState != SelectionState::ExtendedSelection) {
         newSelection = expandSelectionToRespectUserSelectAll(innerNode, VisibleSelection(visiblePos));
     }
 
@@ -618,6 +618,16 @@ bool SelectionController::mouseDownWasSingleClickInSelection() const
     return m_mouseDownWasSingleClickInSelection;
 }
 
+void SelectionController::notifySelectionChanged()
+{
+    if (selection().selectionType() == SelectionType::RangeSelection)
+        m_selectionState = SelectionState::ExtendedSelection;
+    else if (selection().selectionType() == SelectionType::CaretSelection)
+        m_selectionState = SelectionState::PlacedCaret;
+    else
+        m_selectionState = SelectionState::HaveNotStartedSelection;
+}
+
 FrameSelection& SelectionController::selection() const
 {
     return m_frame->selection();