[LazyParseCSS] Ensure UseCounting has parity with strict parsing

third_party/WebKit/Source/core/css/StyleSheetContents.cpp

Index: third_party/WebKit/Source/core/css/StyleSheetContents.cpp
diff --git a/third_party/WebKit/Source/core/css/StyleSheetContents.cpp b/third_party/WebKit/Source/core/css/StyleSheetContents.cpp
index be7d917df767513bc75e55fef728e24855593542..be199485ccd790933f278c6bae8578cab046fac3 100644
--- a/third_party/WebKit/Source/core/css/StyleSheetContents.cpp
+++ b/third_party/WebKit/Source/core/css/StyleSheetContents.cpp
@@ -326,6 +326,12 @@ const AtomicString& StyleSheetContents::namespaceURIFromPrefix(
 void StyleSheetContents::parseAuthorStyleSheet(
     const CSSStyleSheetResource* cachedStyleSheet,
     const SecurityOrigin* securityOrigin) {
+  // All StyleSheetContents are first parsed with a single owner document and
+  // node. This guarantees us that we will always have a valid document for use
+  // counting.
+  DCHECK(hasSingleOwnerDocument());
+  DCHECK(hasSingleOwnerNode());
+
   TRACE_EVENT1("blink,devtools.timeline", "ParseAuthorStyleSheet", "data",
                InspectorParseAuthorStyleSheetEvent::data(cachedStyleSheet));
   double startTimeMS = monotonicallyIncreasingTimeMS();
@@ -491,6 +497,10 @@ Document* StyleSheetContents::singleOwnerDocument() const {
   return root->clientSingleOwnerDocument();
 }
 
+Document* StyleSheetContents::anyOwnerDocument() const {
+  return rootStyleSheet()->clientAnyOwnerDocument();
+}
+
 static bool childRulesHaveFailedOrCanceledSubresources(
     const HeapVector<Member<StyleRuleBase>>& rules) {
   for (unsigned i = 0; i < rules.size(); ++i) {
@@ -531,13 +541,16 @@ bool StyleSheetContents::hasFailedOrCanceledSubresources() const {
   return childRulesHaveFailedOrCanceledSubresources(m_childRules);
 }
 
-Document* StyleSheetContents::clientSingleOwnerDocument() const {
-  if (!m_hasSingleOwnerDocument || clientSize() <= 0)
+Document* StyleSheetContents::clientAnyOwnerDocument() const {
+  if (clientSize() <= 0)
     return nullptr;
+  return m_loadingClients.size()
+             ? (*m_loadingClients.begin())->ownerDocument()
+             : (*m_completedClients.begin())->ownerDocument();

[rune, 2016/12/02 22:18:08]

Nit: is the return rewrite due to the chromium coding style? I think it was more
readable before.

[Charlie Harrison, 2016/12/02 22:38:46]

I can change it back, I was mostly just trying to remove a branch.

[Charlie Harrison, 2016/12/05 19:30:09]

Done.

+}
 
-  if (m_loadingClients.size())
-    return (*m_loadingClients.begin())->ownerDocument();
-  return (*m_completedClients.begin())->ownerDocument();
+Document* StyleSheetContents::clientSingleOwnerDocument() const {
+  return m_hasSingleOwnerDocument ? clientAnyOwnerDocument() : nullptr;
 }
 
 StyleSheetContents* StyleSheetContents::parentStyleSheet() const {