Get rid of inefficient uses of childNodeCount()

Source/core/editing/TextIterator.cpp

 /*
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2005 Alexey Proskuryakov.
  *
  * 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 1165 matching lines @@
     if (!r)
         return;
 
     Node* startNode = r->startContainer();
     if (!startNode)
         return;
     Node* endNode = r->endContainer();
     int startOffset = r->startOffset();
     int endOffset = r->endOffset();
 
-    if (!startNode->offsetInCharacters()) {
-        if (startOffset >= 0 && startOffset < static_cast<int>(startNode->childNodeCount())) {
-            startNode = startNode->childNode(startOffset);
+    if (!startNode->offsetInCharacters() && startOffset >= 0) {
+        // childNode() will return 0 if the offset is out of range. We rely on this behavior
+        // instead of calling childNodeCount() to avoid traversing the children twice.
+        if (Node* childAtOffset = startNode->childNode(startOffset)) {
+            startNode = childAtOffset;
             startOffset = 0;
         }
     }
-    if (!endNode->offsetInCharacters()) {
-        if (endOffset > 0 && endOffset <= static_cast<int>(endNode->childNodeCount())) {
-            endNode = endNode->childNode(endOffset - 1);
+    if (!endNode->offsetInCharacters() && endOffset > 0) {
+        // childNode() will return 0 if the offset is out of range. We rely on this behavior
+        // instead of calling childNodeCount() to avoid traversing the children twice.
+        if (Node* childAtOffset = endNode->childNode(endOffset - 1)) {
+            endNode = childAtOffset;
             endOffset = lastOffsetInNode(endNode);
         }
     }
 
     m_node = endNode;
     setUpFullyClippedStack(m_fullyClippedStack, m_node);
     m_offset = endOffset;
     m_handledNode = false;
     m_handledChildren = !endOffset;
 
@@ skipping 872 matching lines @@
         if (!matchLength)
             return collapsedToBoundary(range, !(options & Backwards));
     }
 
     // Then, find the document position of the start and the end of the text.
     CharacterIterator computeRangeIterator(range, TextIteratorEntersTextControls | TextIteratorEntersAuthorShadowRoots);
     return characterSubrange(computeRangeIterator, matchStart, matchLength);
 }
 
 }