Selection API: Selection.extend() should throw if rangeCount is 0.

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 347 matching lines @@
   frame()->document()->updateStyleAndLayoutIgnorePendingStylesheets();
 
   frame()->selection().modify(alter, direction, granularity);
 }
 
 void DOMSelection::extend(Node* node,
                           int offset,
                           ExceptionState& exceptionState) {
   DCHECK(node);
 
-  if (!isAvailable())
+  if (rangeCount() == 0) {
+    exceptionState.throwDOMException(
+        InvalidStateError, "This Selection object doesn't have any Ranges.");
     return;
+  }
 
   if (offset < 0) {
     exceptionState.throwDOMException(
         IndexSizeError, String::number(offset) + " is not a valid offset.");
     return;
   }
   if (static_cast<unsigned>(offset) > node->lengthOfContents()) {
     exceptionState.throwDOMException(
         IndexSizeError,
         String::number(offset) + " is larger than the given node's length.");
@@ skipping 288 matching lines @@
     m_treeScope->document().addConsoleMessage(
         ConsoleMessage::create(JSMessageSource, ErrorMessageLevel, message));
 }
 
 DEFINE_TRACE(DOMSelection) {
   visitor->trace(m_treeScope);
   ContextClient::trace(visitor);
 }
 
 }  // namespace blink