Reland 'Use FrameSelection::selectedText where possible.'

third_party/WebKit/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 632 matching lines @@
 // TODO(yosin) 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.
 template <typename Strategy>
 void VisibleSelectionTemplate<Strategy>::setWithoutValidation(const PositionTemplate<Strategy>& base, const PositionTemplate<Strategy>& extent)
 {
-    ASSERT(!base.isNull());
-    ASSERT(!extent.isNull());
+    if (base.isNull() || extent.isNull()) {
+        m_base = m_extent = m_start = m_end = PositionTemplate<Strategy>();
+        updateSelectionType();
+        return;
+    }
 
     // TODO(hajimehoshi): We doubt this assertion is needed. This was introduced
     // by http://trac.webkit.org/browser/trunk/WebCore/editing/Selection.cpp?annotate=blame&rev=21071
     ASSERT(m_affinity == TextAffinity::Downstream);
 
     m_base = base;
     m_extent = extent;
     m_baseIsFirst = base.compareTo(extent) <= 0;
     if (m_baseIsFirst) {
         m_start = base;
@@ skipping 468 matching lines @@
 {
     sel.showTreeForThis();
 }
 
 void showTree(const blink::VisibleSelectionInComposedTree* sel)
 {
     if (sel)
         sel->showTreeForThis();
 }
 #endif