HTML Imports: Take care of cycles according to the spec.

Source/core/html/imports/HTMLImportLoader.cpp

Index: Source/core/html/imports/HTMLImportLoader.cpp
diff --git a/Source/core/html/imports/HTMLImportLoader.cpp b/Source/core/html/imports/HTMLImportLoader.cpp
index 155e0964cb527b0886b126c9f7058c84ccf831c1..c24e0c48dc52df713e9996e46e8623d639a071bc 100644
--- a/Source/core/html/imports/HTMLImportLoader.cpp
+++ b/Source/core/html/imports/HTMLImportLoader.cpp
@@ -208,12 +208,7 @@ void HTMLImportLoader::removeImport(HTMLImportChild* client)
 
 bool HTMLImportLoader::shouldBlockScriptExecution() const
 {
-    for (size_t i = 0; i < m_imports.size(); ++i) {
-        if (!m_imports[i]->state().shouldBlockScriptExecution())
-            return false;
-    }
-
-    return true;
+    return firstImport()->state().shouldBlockScriptExecution();
 }
 
 PassRefPtr<CustomElementMicrotaskQueue> HTMLImportLoader::microtaskQueue() const