Do not block painting for in-body CSS

third_party/WebKit/Source/core/dom/StyleElement.cpp

Index: third_party/WebKit/Source/core/dom/StyleElement.cpp
diff --git a/third_party/WebKit/Source/core/dom/StyleElement.cpp b/third_party/WebKit/Source/core/dom/StyleElement.cpp
index b10eff3d83577e17d6bba2bd9746ae1cc8c1f1a8..b84fd77d39d598705900cfea400b29af4e9e9c0a 100644
--- a/third_party/WebKit/Source/core/dom/StyleElement.cpp
+++ b/third_party/WebKit/Source/core/dom/StyleElement.cpp
@@ -47,6 +47,7 @@ StyleElement::StyleElement(Document* document, bool createdByParser)
     : m_createdByParser(createdByParser)
     , m_loading(false)
     , m_registeredAsCandidate(false)
+    , m_beforeBody(false)
     , m_startPosition(TextPosition::belowRangePosition())
 {
     if (createdByParser && document && document->scriptableDocumentParser() && !document->isInDocumentWrite())
@@ -146,7 +147,7 @@ void StyleElement::clearSheet(Element* ownerElement)
     DCHECK(m_sheet);
 
     if (ownerElement && m_sheet->isLoading())
-        ownerElement->document().styleEngine().removePendingSheet(ownerElement);
+        ownerElement->document().styleEngine().removePendingSheet(ownerElement, m_beforeBody);
 
     m_sheet.release()->clearOwnerNode();
 }
@@ -191,7 +192,8 @@ StyleElement::ProcessingResult StyleElement::createSheet(Element* e, const Strin
         if (screenEval.eval(mediaQueries) || printEval.eval(mediaQueries)) {
             m_loading = true;
             TextPosition startPosition = m_startPosition == TextPosition::belowRangePosition() ? TextPosition::minimumPosition() : m_startPosition;
-            newSheet = document.styleEngine().createSheet(e, text, startPosition);
+            m_beforeBody = m_beforeBody || !document.body();

[esprehn, 2016/05/06 21:50:15]

Can we move this into the StyleEngine instead?

[Pat Meenan, 2016/05/09 18:51:05]

The main issue is that we need to keep track of if the sheet was originally
created/requested before the body so when it finishes loading and we remove it
we also decrement the "before body" counter.  The style engine could handle the
part about when it is created but when the sheet is removed it doesn't have the
context to know (at least AFAIK).

It would be possible if the parser didn't keep going after the sheet is created
but as it stands right now, the parser can be before the body when a sheet is
created and after the body when it finishes so the state needed to be attached
to the sheet itself.

+            newSheet = document.styleEngine().createSheet(e, text, startPosition, m_beforeBody);
             newSheet->setMediaQueries(mediaQueries);
             m_loading = false;
         }
@@ -219,13 +221,14 @@ bool StyleElement::sheetLoaded(Document& document)
     if (isLoading())
         return false;
 
-    document.styleEngine().removePendingSheet(m_sheet->ownerNode());
+    document.styleEngine().removePendingSheet(m_sheet->ownerNode(), m_beforeBody);
     return true;
 }
 
 void StyleElement::startLoadingDynamicSheet(Document& document)
 {
-    document.styleEngine().addPendingSheet();
+    m_beforeBody = m_beforeBody || !document.body();
+    document.styleEngine().addPendingSheet(m_beforeBody);
 }
 
 DEFINE_TRACE(StyleElement)