Make SelectionController not to set invalid selection by mouse down

Source/core/editing/VisibleSelection.cpp

 /*
  * Copyright (C) 2004, 2005, 2006 Apple Computer, 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
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 720 matching lines @@
 
 void VisibleSelection::resetPositionsInComposedTree()
 {
     m_baseInComposedTree = toPositionInComposedTree(m_base);
     m_extentInComposedTree = toPositionInComposedTree(m_extent);
     m_endInComposedTree = toPositionInComposedTree(m_end);
     m_startInComposedTree = toPositionInComposedTree(m_start);
     adjustStartAndEndInComposedTree();
 }
 
+bool VisibleSelection::isValidFor(const Document& document) const
+{
+    if (isNone())
+        return true;
+
+    return m_base.document() == &document
+        && !m_base.isOrphan() && !m_extent.isOrphan()
+        && !m_start.isOrphan() && !m_end.isOrphan()
+        && !m_baseInComposedTree.isOrphan() && !m_extentInComposedTree.isOrphan()
+        && !m_startInComposedTree.isOrphan() && !m_endInComposedTree.isOrphan();
+}
+
 // FIXME: This function breaks the invariant of this class.
 // But because we use VisibleSelection to store values in editing commands for use when
 // undoing the command, we need to be able to create a selection that while currently
 // invalid, will be valid once the changes are undone. This is a design problem.
 // To fix it we either need to change the invariants of VisibleSelection or create a new
 // class for editing to use that can manipulate selections that are not currently valid.
 void VisibleSelection::setWithoutValidation(const Position& base, const Position& extent)
 {
     ASSERT(!base.isNull());
     ASSERT(!extent.isNull());
@@ skipping 489 matching lines @@
     sel.showTreeForThis();
 }
 
 void showTree(const blink::VisibleSelection* sel)
 {
     if (sel)
         sel->showTreeForThis();
 }
 
 #endif