Don't start layout for XML just because the root has been opened. And don't

start layout until <html:head> closes if <html:head> gets opened.  For XHTML
documents, this should prevent flashes of unstyled content.

Also, don't flush tags unless forced to if a sheet is pending.

Bug 380028, r+sr=sicking

content/base/src/nsContentSink.cpp

@@ -269,14 +269,20 @@ nsContentSink::StyleSheetLoaded(nsICSSStyleSheet* aSheet,
     NS_ASSERTION(mPendingSheetCount > 0, "How'd that happen?");
     --mPendingSheetCount;
 
-    if (mPendingSheetCount == 0 && mDeferredLayoutStart) {
-      // We might not have really started layout, since this sheet was still
-      // loading.  Do it now.  Probably doesn't matter whether we do this
-      // before or after we unblock scripts, but before feels saner.  Note that
-      // if mDeferredLayoutStart is true, that means any subclass StartLayout()
-      // stuff that needs to happen has already happened, so we don't need to
-      // worry about it.
-      StartLayout(PR_FALSE);
+    if (mPendingSheetCount == 0 &&
+        (mDeferredLayoutStart || mDeferredFlushTags)) {
+      if (mDeferredFlushTags) {
+        FlushTags();
+      }
+      if (mDeferredLayoutStart) {
+        // We might not have really started layout, since this sheet was still
+        // loading.  Do it now.  Probably doesn't matter whether we do this
+        // before or after we unblock scripts, but before feels saner.  Note
+        // that if mDeferredLayoutStart is true, that means any subclass
+        // StartLayout() stuff that needs to happen has already happened, so we
+        // don't need to worry about it.
+        StartLayout(PR_FALSE);
+      }
 
       // Go ahead and try to scroll to our ref if we have one
       TryToScrollToRef();
@@ -1019,7 +1025,7 @@ nsContentSink::StartLayout(PRBool aIgnorePendingSheets)
   
   mDeferredLayoutStart = PR_TRUE;
 
-  if (!aIgnorePendingSheets && mPendingSheetCount > 0) {
+  if (!aIgnorePendingSheets && WaitForPendingSheets()) {
     // Bail out; we'll start layout when the sheets load
     return;
   }
@@ -1172,11 +1178,16 @@ nsContentSink::Notify(nsITimer *timer)
   }
 #endif
 
-  FlushTags();
+  if (WaitForPendingSheets()) {
+    mDeferredFlushTags = PR_TRUE;
+  } else {
+    FlushTags();
+
+    // Now try and scroll to the reference
+    // XXX Should we scroll unconditionally for history loads??
+    TryToScrollToRef();
+  }
 
-  // Now try and scroll to the reference
-  // XXX Should we scroll unconditionally for history loads??
-  TryToScrollToRef();
   mNotificationTimer = nsnull;
   MOZ_TIMER_DEBUGLOG(("Stop: nsHTMLContentSink::Notify()\n"));
   MOZ_TIMER_STOP(mWatch);
@@ -1191,6 +1202,11 @@ nsContentSink::IsTimeToNotify()
     return PR_FALSE;
   }
 
+  if (WaitForPendingSheets()) {
+    mDeferredFlushTags = PR_TRUE;
+    return PR_FALSE;
+  }
+
   PRTime now = PR_Now();
   PRInt64 interval, diff;
 
@@ -1213,7 +1229,9 @@ nsContentSink::WillInterruptImpl()
   SINK_TRACE(gContentSinkLogModuleInfo, SINK_TRACE_CALLS,
              ("nsContentSink::WillInterrupt: this=%p", this));
 #ifndef SINK_NO_INCREMENTAL
-  if (mNotifyOnTimer && mLayoutStarted) {
+  if (WaitForPendingSheets()) {
+    mDeferredFlushTags = PR_TRUE;
+  } else if (mNotifyOnTimer && mLayoutStarted) {
     if (mBackoffCount && !mInMonolithicContainer) {
       PRInt64 now = PR_Now();
       PRInt64 interval = GetNotificationInterval();

content/base/src/nsContentSink.h

@@ -211,6 +211,10 @@ protected:
 
   void TryToScrollToRef();
 
+  // Later on we might want to make this more involved somehow
+  // (e.g. stop waiting after some timeout or whatnot).
+  PRBool WaitForPendingSheets() { return mPendingSheetCount > 0; }
+
 private:
   // People shouldn't be allocating this class directly.  All subclasses should
   // be allocated using a zeroing operator new.
@@ -276,7 +280,9 @@ protected:
   PRUint8 mHaveOfflineResources : 1;
   // true if offline-resource links should be saved to the offline cache
   PRUint8 mSaveOfflineResources : 1;
-
+  // If true, we deferred notifications until sheets load
+  PRUint8 mDeferredFlushTags : 1;
+  
   // -- Can interrupt parsing members --
   PRUint32 mDelayTimerStart;
 

content/html/document/src/nsHTMLContentSink.cpp

@@ -1340,6 +1340,7 @@ SinkContext::AddText(const nsAString& aText)
 nsresult
 SinkContext::FlushTags()
 {
+  mSink->mDeferredFlushTags = PR_FALSE;
   PRBool oldBeganUpdate = mSink->mBeganUpdate;
   PRUint32 oldUpdates = mSink->mUpdatesInNotification;
 

content/xml/document/src/nsXMLContentSink.cpp

@@ -1066,17 +1066,24 @@ nsXMLContentSink::HandleStartElement(const PRUnichar *aName,
 
   // Some HTML nodes need DoneCreatingElement() called to initialize
   // properly (eg form state restoration).
-  if (nodeInfo->NamespaceID() == kNameSpaceID_XHTML &&
-      (nodeInfo->NameAtom() == nsGkAtoms::input ||
-       nodeInfo->NameAtom() == nsGkAtoms::button)) {
-    content->DoneCreatingElement();
+  if (nodeInfo->NamespaceID() == kNameSpaceID_XHTML) {
+    if (nodeInfo->NameAtom() == nsGkAtoms::input ||
+        nodeInfo->NameAtom() == nsGkAtoms::button) {
+      content->DoneCreatingElement();
+    } else if (nodeInfo->NameAtom() == nsGkAtoms::head && !mCurrentHead) {
+      mCurrentHead = content;
+    }
   }
 
   if (IsMonolithicContainer(nodeInfo)) {
     mInMonolithicContainer++;
   }
 
-  MaybeStartLayout(PR_FALSE);
+  if (content != mDocElement && !mCurrentHead) {
+    // This isn't the root and we're not inside an XHTML <head>.
+    // Might need to start layout
+    MaybeStartLayout(PR_FALSE);
+  }
 
   return aInterruptable && NS_SUCCEEDED(result) ? DidProcessATokenImpl() :
                                                   result;
@@ -1122,10 +1129,17 @@ nsXMLContentSink::HandleEndElement(const PRUnichar *aName,
 
   result = CloseElement(content);
 
+  if (mCurrentHead == content) {
+    mCurrentHead = nsnull;
+  }
+  
   if (mDocElement == content) {
     // XXXbz for roots that don't want to be appended on open, we
     // probably need to deal here.... (and stop appending them on open).
     mState = eXMLContentSinkState_InEpilog;
+
+    // We might have had no occasion to start layout yet.  Do so now.
+    MaybeStartLayout(PR_FALSE);
   }
 
   PRInt32 stackLen = mContentStack.Length();
@@ -1591,6 +1605,7 @@ nsXMLContentSink::FlushPendingNotifications(mozFlushType aType)
 nsresult
 nsXMLContentSink::FlushTags()
 {
+  mDeferredFlushTags = PR_FALSE;
   PRBool oldBeganUpdate = mBeganUpdate;
   PRUint32 oldUpdates = mUpdatesInNotification;
 

content/xml/document/src/nsXMLContentSink.h

@@ -183,6 +183,7 @@ protected:
                                PRBool aInterruptable);
 
   nsIContent*      mDocElement;
+  nsCOMPtr<nsIContent> mCurrentHead;  // When set, we're in an XHTML <haed>
   PRUnichar*       mText;
 
   XMLContentSinkState mState;