Remove the concept of user stylesheets.

Source/core/css/StyleRuleImport.cpp

Index: Source/core/css/StyleRuleImport.cpp
diff --git a/Source/core/css/StyleRuleImport.cpp b/Source/core/css/StyleRuleImport.cpp
index 5167a4280bd84a34391c63a2e165bf532aec28cc..1038edf11f7248cf4d32092f3f7b800846cdd237 100644
--- a/Source/core/css/StyleRuleImport.cpp
+++ b/Source/core/css/StyleRuleImport.cpp
@@ -115,10 +115,7 @@ void StyleRuleImport::requestStyleSheet()
     }
 
     FetchRequest request(ResourceRequest(absURL), FetchInitiatorTypeNames::css, m_parentStyleSheet->charset());
-    if (m_parentStyleSheet->isUserStyleSheet())
-        m_resource = fetcher->fetchUserCSSStyleSheet(request);
-    else
-        m_resource = fetcher->fetchCSSStyleSheet(request);
+    m_resource = fetcher->fetchCSSStyleSheet(request);
     if (m_resource) {
         // if the import rule is issued dynamically, the sheet may be
         // removed from the pending sheet count, so let the doc know