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

Source/core/editing/SelectionController.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2006 Alexey Proskuryakov (ap@webkit.org)
  * Copyright (C) 2012 Digia Plc. and/or its subsidiary(-ies)
  * Copyright (C) 2015 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
@@ skipping 175 matching lines @@
                     newSelection = VisibleSelection(start, pos);
             }
         } else {
             newSelection.setExtent(pos);
         }
 
         if (selection().granularity() != CharacterGranularity) {
             granularity = selection().granularity();
             expandSelectionUsingGranularity(newSelection, selection().granularity());
         }
-    } else {
+    } else if (m_selectionState != SelectionState::ExtendedSelection) {
         newSelection = expandSelectionToRespectUserSelectAll(innerNode, VisibleSelection(visiblePos));
     }
 
     // Updating the selection is considered side-effect of the event and so it doesn't impact the handled state.
     updateSelectionForMouseDownDispatchingSelectStart(innerNode, newSelection, granularity);
     return false;
 }
 
 template <typename Strategy>
 void SelectionController::updateSelectionForMouseDragAlgorithm(const HitTestResult& hitTestResult, Node* mousePressNode, const LayoutPoint& dragStartPos, const IntPoint& lastKnownMousePosition)
@@ skipping 404 matching lines @@
 bool SelectionController::mouseDownMayStartSelect() const
 {
     return m_mouseDownMayStartSelect;
 }
 
 bool SelectionController::mouseDownWasSingleClickInSelection() const
 {
     return m_mouseDownWasSingleClickInSelection;
 }
 
+void SelectionController::notifySelectionChanged()
+{

[yosin_UTC9, 2015/07/06 01:57:30]

It is better to have a function which maps |SelectionType| to |SelectionState|.
Or, use |SelectionType| instead of |SelectionState|.

BTW, what difference between |m_selectionState| and
|m_frame->selection().selection().selectionType()|? Do we need to keep tracking
selection type in both |FrameSelection| and |SelectionController|?

[Miyoung Shin(g), 2015/07/13 03:32:57]

Done.
IIUC, |m_selectionState| works together for events so it can be changed to the
range status as |m_frame->selection().selection().selectionType()| is not the
range yet.
eg. when starting dragging the mouse on text, |m_selectionState| is set to
|SelectionState::ExtendedSelection| first in
|SelectionController::updateSelectionForMouseDragAlgorithm|. At that time,
|selectionType()| is still |SelectionType::CaretSelection|.
And then, when handling the next mouse event we can keep the selection range.

Also, even if |selectionType()| is |SelectionType::RangeSelection| when handling
the mouse release event, we can clear the selection through |m_selectionState|.

+    if (selection().isRange())
+        m_selectionState = SelectionState::ExtendedSelection;
+    else if (selection().isCaret())
+        m_selectionState = SelectionState::PlacedCaret;
+    else
+        m_selectionState = SelectionState::HaveNotStartedSelection;
+}
+
 FrameSelection& SelectionController::selection() const
 {
     return m_frame->selection();
 }
 
 } // namespace blink