Stop SpellChecker from adding marker when checking range is modified

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

 /*
  * Copyright (C) 2006, 2007, 2008, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2008 Nokia Corporation and/or its subsidiary(-ies)
  *
  * 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
@@ skipping 612 matching lines @@
     return;
   }
 
   // TODO(xiaochengh): The use of updateStyleAndLayoutIgnorePendingStylesheets
   // needs to be audited.  See http://crbug.com/590369 for more details.
   frame().document()->updateStyleAndLayoutIgnorePendingStylesheets();
 
   DocumentLifecycle::DisallowTransitionScope disallowTransition(
       frame().document()->lifecycle());
 
-  TextCheckingParagraph paragraph(request->checkingRange(),
-                                  request->checkingRange());
+  EphemeralRange checkingRange(request->checkingRange());
+
+  // Abort marking if the content of the checking change has been modified.
+  String currentContent =
+      plainText(checkingRange,
+                TextIteratorBehavior::Builder()
+                    .setEmitsObjectReplacementCharacter(true)
+                    .build());
+  if (currentContent != request->data().text()) {
+    // "editing/spelling/spellcheck-async-mutation.html" reaches here.
+    return;
+  }
+
+  TextCheckingParagraph paragraph(checkingRange, checkingRange);
 
   // TODO(xiaochengh): The following comment does not match the current behavior
   // and should be rewritten.
   // Expand the range to encompass entire paragraphs, since text checking needs
   // that much context.
   int selectionOffset = 0;
   int ambiguousBoundaryOffset = -1;
 
   if (frame()
           .selection()
@@ skipping 573 matching lines @@
         startOfNextParagraph(createVisiblePosition(paragraphEnd));
     paragraphStart = newParagraphStart.toParentAnchoredPosition();
     paragraphEnd = endOfParagraph(newParagraphStart).toParentAnchoredPosition();
     firstIteration = false;
     totalLengthProcessed += currentLength;
   }
   return std::make_pair(firstFoundItem, firstFoundOffset);
 }
 
 }  // namespace blink