Avoid unnecessary copies of AccessibilityChildrenVector

Source/modules/accessibility/AXObjectCacheImpl.cpp

 /*
  * Copyright (C) 2014, 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.
  * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 109 matching lines @@
         return 0;
 
     HTMLImageElement* imageElement = areaElement->imageElement();
     if (!imageElement)
         return 0;
 
     AXObject* axLayoutImage = getOrCreate(imageElement);
     if (!axLayoutImage)
         return 0;
 
-    AXObject::AccessibilityChildrenVector imageChildren = axLayoutImage->children();
+    const AXObject::AccessibilityChildrenVector& imageChildren = axLayoutImage->children();
     unsigned count = imageChildren.size();
     for (unsigned k = 0; k < count; ++k) {
         AXObject* child = imageChildren[k].get();
         if (!child->isImageMapLink())
             continue;
 
         if (toAXImageMapLink(child)->areaElement() == areaElement)
             return child;
     }
 
@@ skipping 980 matching lines @@
 void AXObjectCacheImpl::setCanvasObjectBounds(Element* element, const LayoutRect& rect)
 {
     AXObject* obj = getOrCreate(element);
     if (!obj)
         return;
 
     obj->setElementRect(rect);
 }
 
 } // namespace blink