Fix <dialog> centering

Source/WebCore/rendering/RenderDialog.cpp

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 22 matching lines @@
 #include "RenderView.h"
 
 namespace WebCore {
 
 void RenderDialog::layout()
 {
     StackStats::LayoutCheckPoint layoutCheckPoint;
     LayoutRepainter repainter(*this, true);
     LayoutStateMaintainer statePusher(view(), this, locationOffset(), hasTransform() || hasReflection() || style()->isFlippedBlocksWritingMode());
 
+    bool hadLayout = everHadLayout();
+    if (hadLayout) {
+        if (layer())
+            layer()->setStaticBlockPosition(m_staticBlockPos);
+    }
     RenderBlock::layout();
 
     RenderStyle* styleToUse = style();
-    if (styleToUse->position() != AbsolutePosition || !styleToUse->top().isAuto() || !styleToUse->bottom().isAuto()) {
+    if ((styleToUse->position() != AbsolutePosition && styleToUse->position() != RelativePosition) || !styleToUse->top().isAuto() || !styleToUse->bottom().isAuto()) {
         statePusher.pop();
         return;
     }
 
-    // Adjust the dialog's position to be centered in or at the top of the viewport.
-    // FIXME: Figure out what to do in vertical writing mode.
-    FrameView* frameView = document()->view();
-    int scrollTop = frameView->scrollOffset().height();
-    FloatPoint absolutePoint(0, scrollTop);
-    int visibleHeight = frameView->visibleContentRect(ScrollableArea::IncludeScrollbars).height();
-    if (height() < visibleHeight)
-        absolutePoint.move(0, (visibleHeight - height()) / 2);
-    FloatPoint localPoint = containingBlock()->absoluteToLocal(absolutePoint);
-    LayoutUnit localTop = LayoutSize(localPoint.x(), localPoint.y()).height();
-    setY(localTop);
+    if (!hadLayout) {
+        FrameView* frameView = document()->view();
+        int scrollTop = frameView->scrollOffset().height();
+        FloatPoint absolutePoint(0, scrollTop);
+        int visibleHeight = frameView->visibleContentRect(ScrollableArea::IncludeScrollbars).height();
+        if (height() < visibleHeight)
+            absolutePoint.move(0, (visibleHeight - height()) / 2);
+        FloatPoint localPoint = containingBlock()->absoluteToLocal(absolutePoint);
+        LayoutUnit localTop = LayoutSize(localPoint.x(), localPoint.y()).height();
 
+        m_staticBlockPos = localTop;
+        layer()->setStaticBlockPosition(m_staticBlockPos);
+        setNeedsLayout(true);
+        RenderBlock::layout();
+    } else {
+        ASSERT(layer()->staticBlockPosition() == m_staticBlockPos);
+    }
     statePusher.pop();
-    // FIXME: Since there is always a layer here, repainter shouldn't be necessary. But without it, the dialog is sometimes not painted (see bug 90670).
     repainter.repaintAfterLayout();
 }
 
 }
 
 #endif