add 'slow' prefix to RenderObject's firstChild() / lastChild() methods

Source/core/plugins/PluginOcclusionSupport.cpp

Index: Source/core/plugins/PluginOcclusionSupport.cpp
diff --git a/Source/core/plugins/PluginOcclusionSupport.cpp b/Source/core/plugins/PluginOcclusionSupport.cpp
index f5541414c6b74cf09e27e976513709ebe8b8ecf4..8a3ce869ecebf62c13ef0c38f23460d03a64183f 100644
--- a/Source/core/plugins/PluginOcclusionSupport.cpp
+++ b/Source/core/plugins/PluginOcclusionSupport.cpp
@@ -100,7 +100,7 @@ static bool iframeIsAbovePlugin(const Vector<const RenderObject*>& iframeZstack,
                 return false;
             ASSERT(parent == ro2->parent());
 
-            for (const RenderObject* ro = parent->firstChild(); ro; ro = ro->nextSibling()) {
+            for (const RenderObject* ro = parent->slowFirstChild(); ro; ro = ro->nextSibling()) {
                 if (ro == ro1)
                     return false;
                 if (ro == ro2)
@@ -132,7 +132,7 @@ static void addTreeToOcclusions(const RenderObject* renderer, const IntRect& fra
         return;
     if (renderer->isBox() && intersectsRect(renderer, frameRect))
         addToOcclusions(toRenderBox(renderer), occlusions);
-    for (RenderObject* child = renderer->firstChild(); child; child = child->nextSibling())
+    for (RenderObject* child = renderer->slowFirstChild(); child; child = child->nextSibling())
         addTreeToOcclusions(child, frameRect, occlusions);
 }