Remove forward declarations from Source/core/dom/custom

Source/core/dom/custom/CustomElementProcessingStack.h

Index: Source/core/dom/custom/CustomElementProcessingStack.h
diff --git a/Source/core/dom/custom/CustomElementProcessingStack.h b/Source/core/dom/custom/CustomElementProcessingStack.h
index 551ce97a87d1a06feb3d5f17b8ddb50ea5fa215d..742d3d536b83e398bead9933f00c2f4a27210c6e 100644
--- a/Source/core/dom/custom/CustomElementProcessingStack.h
+++ b/Source/core/dom/custom/CustomElementProcessingStack.h
@@ -36,8 +36,6 @@
 
 namespace blink {
 
-class CustomElementScheduler;
-
 class CustomElementProcessingStack {
     WTF_MAKE_NONCOPYABLE(CustomElementProcessingStack);
 public:
@@ -100,6 +98,6 @@ private:
     Vector<CustomElementCallbackQueue*> m_flattenedProcessingStack;
 };
 
-}
+} // namespace blink
 
 #endif // CustomElementProcessingStack_h