Stop crashing when VisibleSelections in DOM and Flat trees are inconsistent

third_party/WebKit/Source/core/editing/FrameSelection.cpp

 /*
  * Copyright (C) 2004, 2008, 2009, 2010 Apple 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 411 matching lines @@
   granularity_ = kCharacterGranularity;
   if (granularity_strategy_)
     granularity_strategy_->Clear();
   SetSelection(SelectionInDOMTree());
 }
 
 bool FrameSelection::SelectionHasFocus() const {
   // TODO(editing-dev): Hoist UpdateStyleAndLayoutIgnorePendingStylesheets
   // to caller. See http://crbug.com/590369 for more details.
   GetDocument().UpdateStyleAndLayoutIgnorePendingStylesheets();
+  if (ComputeVisibleSelectionInFlatTree().IsNone())
+    return false;
   const Node* current =
-      ComputeVisibleSelectionInDOMTree().Start().ComputeContainerNode();
+      ComputeVisibleSelectionInFlatTree().Start().ComputeContainerNode();
   if (!current)
     return false;
 
   // No focused element means document root has focus.
   Element* const focused_element = GetDocument().FocusedElement()
                                        ? GetDocument().FocusedElement()
                                        : GetDocument().documentElement();
   if (!focused_element)
     return false;
 
   if (focused_element->IsTextControl())
     return focused_element->ContainsIncludingHostElements(*current);
 
-  if (ComputeVisibleSelectionInFlatTree().IsNone()) {
-    // TODO(editing-dev): We should avoid any case where VSInFlatTree is none
-    // but VSInDOMTree is not none.
-    DLOG(FATAL) << ComputeVisibleSelectionInDOMTree();
-  }
-
   // Selection has focus if it contains the focused element.
   const PositionInFlatTree& focused_position =
       PositionInFlatTree::FirstPositionInNode(focused_element);
   if (ComputeVisibleSelectionInFlatTree().Start() <= focused_position &&
       ComputeVisibleSelectionInFlatTree().End() >= focused_position)
     return true;
 
   bool has_editable_style = HasEditableStyle(*current);
   do {
     // If the selection is within an editable sub tree and that sub tree
@@ skipping 723 matching lines @@
 }
 
 void showTree(const blink::FrameSelection* sel) {
   if (sel)
     sel->ShowTreeForThis();
   else
     LOG(INFO) << "Cannot showTree for <null> FrameSelection.";
 }
 
 #endif