Correct usage of text iterator in idle time spellchecker

third_party/WebKit/Source/core/editing/spellcheck/HotModeSpellCheckRequester.cpp

 // Copyright 2017 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/editing/spellcheck/HotModeSpellCheckRequester.h"
 
 #include "core/editing/EditingUtilities.h"
 #include "core/editing/Editor.h"
 #include "core/editing/VisiblePosition.h"
 #include "core/editing/commands/CompositeEditCommand.h"
@@ skipping 55 matching lines @@
   const int fullLength = TextIterator::rangeLength(fullRange.startPosition(),
                                                    fullRange.endPosition());
   if (fullLength <= kHotModeChunkSize)
     return fullRange;
 
   TextIteratorBehavior behavior = TextIteratorBehavior::Builder()
                                       .setEmitsObjectReplacementCharacter(true)
                                       .build();
   BackwardsCharacterIterator backwardIterator(fullRange.startPosition(),
                                               position, behavior);
-  backwardIterator.advance(kHotModeChunkSize / 2);
+  if (!backwardIterator.atEnd())
+    backwardIterator.advance(kHotModeChunkSize / 2);
   const Position& chunkStart = backwardIterator.endPosition();
   CharacterIterator forwardIterator(position, fullRange.endPosition(),
                                     behavior);
-  forwardIterator.advance(kHotModeChunkSize / 2);
+  if (!forwardIterator.atEnd())
+    forwardIterator.advance(kHotModeChunkSize / 2);
   const Position& chunkEnd = forwardIterator.endPosition();
   return expandRangeToSentenceBoundary(EphemeralRange(chunkStart, chunkEnd));
 }
 
 }  // namespace
 
 HotModeSpellCheckRequester::HotModeSpellCheckRequester(
     SpellCheckRequester& requester)
     : m_requester(requester) {}
 
 void HotModeSpellCheckRequester::checkSpellingAt(const Position& position) {
   const Element* rootEditable = rootEditableElementOf(position);
   if (!rootEditable || !rootEditable->isConnected())
     return;
 
   if (m_processedRootEditables.contains(rootEditable))
     return;
   m_processedRootEditables.push_back(rootEditable);
 
   if (!shouldCheckRootEditableInHotMode(*rootEditable, position))
     return;
 
   SpellCheckRequest* request = SpellCheckRequest::create(
       calculateHotModeCheckingRange(*rootEditable, position));
   m_requester->requestCheckingFor(request);
 }
 
 }  // namespace blink