Extract tree root responsibility out of HTMLImportsController.

Source/core/html/imports/LinkImport.cpp

Index: Source/core/html/imports/LinkImport.cpp
diff --git a/Source/core/html/imports/LinkImport.cpp b/Source/core/html/imports/LinkImport.cpp
index 6183852fd13eb402102b0593ec0990a99803b4ef..9265f86f7b5183e2c62627f2900f0c6c4f84fdf5 100644
--- a/Source/core/html/imports/LinkImport.cpp
+++ b/Source/core/html/imports/LinkImport.cpp
@@ -36,9 +36,9 @@
 #include "core/html/HTMLLinkElement.h"
 #include "core/html/imports/HTMLImportChild.h"
 #include "core/html/imports/HTMLImportLoader.h"
+#include "core/html/imports/HTMLImportTreeRoot.h"
 #include "core/html/imports/HTMLImportsController.h"
 
-
 namespace WebCore {
 
 PassOwnPtrWillBeRawPtr<LinkImport> LinkImport::create(HTMLLinkElement* owner)
@@ -89,7 +89,7 @@ void LinkImport::process()
 
     HTMLImportsController* controller = m_owner->document().importsController();
     HTMLImportLoader* loader = m_owner->document().importLoader();
-    HTMLImport* parent = loader ? static_cast<HTMLImport*>(loader->firstImport()) : static_cast<HTMLImport*>(controller);
+    HTMLImport* parent = loader ? static_cast<HTMLImport*>(loader->firstImport()) : static_cast<HTMLImport*>(controller->root());
     m_child = controller->load(parent, this, builder.build(true));
     if (!m_child) {
         didFinish();