Introduce use counters for shadow DOM handling in plainText()

Source/core/editing/iterators/CharacterIterator.cpp

Index: Source/core/editing/iterators/CharacterIterator.cpp
diff --git a/Source/core/editing/iterators/CharacterIterator.cpp b/Source/core/editing/iterators/CharacterIterator.cpp
index 232ab7095924a20a7fd9dc3f7084350db2c5cc32..2d9776204e2f5ff11f8abd6206a1eb42708d7681 100644
--- a/Source/core/editing/iterators/CharacterIterator.cpp
+++ b/Source/core/editing/iterators/CharacterIterator.cpp
@@ -628,7 +628,10 @@ void findPlainText(const Position& inputStart, const Position& inputEnd, const S
     size_t matchStart;
     size_t matchLength;
     {
-        CharacterIterator findIterator(inputStart, inputEnd, iteratorFlagsForFindPlainText);
+        TextIteratorBehaviorFlags behavior = iteratorFlagsForFindPlainText;
+        if (options & FindAPICall)
+            behavior |= TextIteratorForWindowFind;
+        CharacterIterator findIterator(inputStart, inputEnd, behavior);
         matchLength = findPlainTextInternal(findIterator, target, options, matchStart);
         if (!matchLength) {
             const Position& collapseTo = options & Backwards ? inputStart : inputEnd;