Make HTMLImportTreeNode own the whole import tree.

Source/core/html/imports/HTMLImport.h

 /*
  * Copyright (C) 2013 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 38 matching lines @@
 //
 // ## The Import Tree
 //
 // HTML Imports form a tree:
 //
 // * The root of the tree is HTMLImportTreeRoot.
 //
 // * The HTMLImportTreeRoot is owned HTMLImportsController, which is owned by the master
 //   document as a DocumentSupplement.
 //
-// * The non-root nodes are HTMLImportChild. They are also owned by HTMLImportsController.
+// * The non-root nodes are HTMLImportChild. They are all owned by HTMLImporTreeRoot.
 //   LinkStyle is wired into HTMLImportChild by implementing HTMLImportChildClient interface
 //
 // * Both HTMLImportTreeRoot and HTMLImportChild are derived from HTMLImport superclass
 //   that models the tree data structure using WTF::TreeNode and provides a set of
 //   virtual functions.
 //
 // HTMLImportsController also owns all loaders in the tree and manages their lifetime through it.
 // One assumption is that the tree is append-only and nodes are never inserted in the middle of the tree nor removed.
 //
+// Full diagram is here:
+// https://docs.google.com/drawings/d/1jFQrO0IupWrlykTNzQ3Nv2SdiBiSz4UE9-V3-vDgBb0/
 //
 // # Import Sharing and HTMLImportLoader
 //
 // The HTML Imports spec calls for de-dup mechanism to share already loaded imports.
 // To implement this, the actual loading machinery is split out from HTMLImportChild to
 // HTMLImportLoader, and each loader shares HTMLImportLoader with other loader if the URL is same.
 // Check around HTMLImportsController::findLink() for more detail.
 //
 // HTMLImportLoader can be shared by multiple imports.
 //
@@ skipping 55 matching lines @@
 #endif
 
 private:
     HTMLImportState m_state;
     unsigned m_sync : 1;
 };
 
 } // namespace WebCore
 
 #endif // HTMLImport_h