DevTools: allow builds with asserions when using DevTools front-end.

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

 /*
  * Copyright (C) 2007, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2012 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
  *     notice, this list of conditions and the following disclaimer.
@@ skipping 365 matching lines @@
         return nullptr;
     }
 
     // If you're hitting this, you've added broken multi-range selection support
     ASSERT(rangeCount() == 1);
 
     Position anchor = anchorPosition(visibleSelection());
     if (!anchor.anchorNode()->isInShadowTree())
         return m_frame->selection().firstRange();
 
+    Node* node = shadowAdjustedNode(anchor);
+    if (!node) // crbug.com/595100

[yosin_UTC9, 2016/04/07 01:25:39]

Could you add a layout test for this case and for avoiding regression in future?
It seems we should change |shadowAdjustedNode()| not to return |nullptr|,
in theory, |shadowAdjustedNode()| should not be |nullptr|.

+        return nullptr;
     if (!visibleSelection().isBaseFirst())
-        return Range::create(*anchor.document(), focusNode(), focusOffset(), shadowAdjustedNode(anchor), anchorOffset());
-    return Range::create(*anchor.document(), shadowAdjustedNode(anchor), anchorOffset(), focusNode(), focusOffset());
+        return Range::create(*anchor.document(), focusNode(), focusOffset(), node, anchorOffset());
+    return Range::create(*anchor.document(), node, anchorOffset(), focusNode(), focusOffset());
 }
 
 void DOMSelection::removeAllRanges()
 {
     if (!m_frame)
         return;
     m_frame->selection().clear();
 }
 
 void DOMSelection::addRange(Range* newRange)
@@ skipping 167 matching lines @@
         m_treeScope->document().addConsoleMessage(ConsoleMessage::create(JSMessageSource, ErrorMessageLevel, message));
 }
 
 DEFINE_TRACE(DOMSelection)
 {
     visitor->trace(m_treeScope);
     DOMWindowProperty::trace(visitor);
 }
 
 } // namespace blink