Allow <link rel=stylesheet> in a connected shadow tree

third_party/WebKit/Source/core/html/HTMLLinkElement.cpp

Index: third_party/WebKit/Source/core/html/HTMLLinkElement.cpp
diff --git a/third_party/WebKit/Source/core/html/HTMLLinkElement.cpp b/third_party/WebKit/Source/core/html/HTMLLinkElement.cpp
index eba8125c3c599b64990771d178a5689e7d0130ca..a57dac24c4bc5da3950f70580568643e500f307f 100644
--- a/third_party/WebKit/Source/core/html/HTMLLinkElement.cpp
+++ b/third_party/WebKit/Source/core/html/HTMLLinkElement.cpp
@@ -133,7 +133,7 @@ void HTMLLinkElement::parseAttribute(const QualifiedName& name, const AtomicStri
 
 bool HTMLLinkElement::shouldLoadLink()
 {
-    return isConnected();
+    return isInDocumentTree() || (isConnected() && m_relAttribute.isStyleSheet());
 }
 
 bool HTMLLinkElement::loadLink(const String& type, const String& as, const String& media, const KURL& url)
@@ -143,8 +143,7 @@ bool HTMLLinkElement::loadLink(const String& type, const String& as, const Strin
 
 LinkResource* HTMLLinkElement::linkResourceToProcess()
 {
-    bool visible = isConnected() && !isInShadowTree();
-    if (!visible) {
+    if (!shouldLoadLink()) {
         ASSERT(!linkStyle() || !linkStyle()->hasSheet());
         return nullptr;
     }
@@ -204,7 +203,7 @@ Node::InsertionNotificationRequest HTMLLinkElement::insertedInto(ContainerNode*
     if (!insertionPoint->isConnected())
         return InsertionDone;
 
-    if (isInShadowTree()) {
+    if (isConnected() && !shouldLoadLink()) {

[kochi, 2016/07/26 05:35:06]

Does insertionPoint->isConnected() on line 203 guarantee that this node is also
connected?
Then isConnected() here is unnecessary.

[hayato, 2016/07/26 06:04:32]

Good point.
I have added DCHECK()s around here.

         String message = "HTML element <link> is ignored in shadow tree.";
         document().addConsoleMessage(ConsoleMessage::create(JSMessageSource, WarningMessageLevel, message));
         return InsertionDone;
@@ -222,15 +221,15 @@ Node::InsertionNotificationRequest HTMLLinkElement::insertedInto(ContainerNode*
 
 void HTMLLinkElement::removedFrom(ContainerNode* insertionPoint)
 {
-    // Store the result of isInShadowTree() here before Node::removedFrom(..) clears the flags.
-    bool wasInShadowTree = isInShadowTree();
+    // Store the result of isConnected() here before Node::removedFrom(..) clears the flags.
+    bool wasConnected = isConnected();
     HTMLElement::removedFrom(insertionPoint);
     if (!insertionPoint->isConnected())
         return;
 
     m_linkLoader->released();
 
-    if (wasInShadowTree) {
+    if (!wasConnected) {
         ASSERT(!linkStyle() || !linkStyle()->hasSheet());
         return;
     }
@@ -440,8 +439,8 @@ enum StyleSheetCacheStatus {
 
 void LinkStyle::setCSSStyleSheet(const String& href, const KURL& baseURL, const String& charset, const CSSStyleSheetResource* cachedStyleSheet)
 {
-    if (!m_owner->isInDocumentTree()) {
-        // While the stylesheet is asynchronously loading, the owner can be moved out of a document tree.
+    if (!m_owner->isConnected()) {
+        // While the stylesheet is asynchronously loading, the owner can be disconnected from a document.
         // In that case, cancel any processing on the loaded content.
         m_loading = false;
         removePendingSheet();
@@ -663,7 +662,8 @@ void LinkStyle::process()
 
         bool mediaQueryMatches = true;
         LocalFrame* frame = loadingFrame();
-        if (!m_owner->media().isEmpty() && frame && frame->document()) {
+        // MediaQuery is valid only in a document tree.

[kochi, 2016/07/26 05:35:06]

Is this a TODO, or defined in any spec?

[hayato, 2016/07/26 06:04:32]

Ops. That was my misunderstanding. I though this as if
https://github.com/w3c/webcomponents/issues/391. My memory is limited. :)
Let me update the patch.

+        if (m_owner->isInDocumentTree() && !m_owner->media().isEmpty() && frame && frame->document()) {
             RefPtr<ComputedStyle> documentStyle = StyleResolver::styleForDocument(*frame->document());
             MediaQuerySet* media = MediaQuerySet::create(m_owner->media());
             MediaQueryEvaluator evaluator(frame);