Clean up forward declarations in Source/core/editing

Source/core/editing/Editor.h

Index: Source/core/editing/Editor.h
diff --git a/Source/core/editing/Editor.h b/Source/core/editing/Editor.h
index 4008c057e7b4c601d9184f38cec3514b46b3333b..a5c7ff7cf9931d5e08746be248d688af3a28c89b 100644
--- a/Source/core/editing/Editor.h
+++ b/Source/core/editing/Editor.h
@@ -42,21 +42,15 @@
 namespace blink {
 
 class CompositeEditCommand;
-class DataTransfer;
-class EditCommand;
 class EditCommandComposition;
 class EditorClient;
 class EditorInternalCommand;
 class LocalFrame;
-class HTMLElement;
 class HitTestResult;
 class KillRing;
 class Pasteboard;
-class SharedBuffer;
-class SimpleFontData;
 class SpellChecker;
 class StylePropertySet;
-class Text;
 class TextEvent;
 class UndoStack;