Extract tree root responsibility out of HTMLImportsController.

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 33 matching lines @@
 class HTMLImportsController;
 class KURL;
 
 //
 // # Basic Data Structure and Algorithms of HTML Imports implemenation.
 //
 // ## The Import Tree
 //
 // HTML Imports form a tree:
 //
-// * The root of the tree is HTMLImportsController, which is owned by the master
+// * 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, which is owned by LinkStyle, that is owned by HTMLLinkElement.
+// * The non-root nodes are HTMLImportChild. They are also owned by HTMLImportsController.
 //   LinkStyle is wired into HTMLImportChild by implementing HTMLImportChildClient interface
 //
-// * Both HTMLImportsController and HTMLImportChild are derived from HTMLImport superclass
+// * 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.
 //
 //
-//    HTMLImport <|- HTMLImportsController <- Document
-//                   *
-//                   |
-//               <|- HTMLImportChild <- LinkStyle <- HTMLLinkElement
-//
-//
 // # 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.
 //
 //    HTMLImportChild (1)-->(*) HTMLImportLoader
 //
 //
 // # Script Blocking
 //
 // - An import blocks the HTML parser of its own imported document from running <script>
 //   until all of its children are loaded.
 //   Note that dynamically added import won't block the parser.
 //
 // - An import under loading also blocks imported documents that follow from being created.
 //   This is because an import can include another import that has same URLs of following ones.
 //   In such case, the preceding import should be loaded and following ones should be de-duped.
 //
 
-// The superclass of HTMLImportsController and HTMLImportChild
+// The superclass of HTMLImportTreeRoot and HTMLImportChild
 // This represents the import tree data structure.
 class HTMLImport : public TreeNode<HTMLImport> {
 public:
     enum SyncMode {
         Sync  = 0,
         Async = 1
     };
 
     virtual ~HTMLImport() { }
 
+    // FIXME: Consider returning HTMLImportTreeRoot.
     HTMLImport* root();
     bool precedes(HTMLImport*);
     bool isRoot() const { return !isChild(); }
     bool isSync() const { return SyncMode(m_sync) == Sync; }
     bool formsCycle() const;
     const HTMLImportState& state() const { return m_state; }
 
     void appendImport(HTMLImport*);
 
     virtual bool isChild() const { return false; }
@@ skipping 19 matching lines @@
 #endif
 
 private:
     HTMLImportState m_state;
     unsigned m_sync : 1;
 };
 
 } // namespace WebCore
 
 #endif // HTMLImport_h