Fix <dialog> centering

Source/WebCore/rendering/RenderDialog.cpp

Index: Source/WebCore/rendering/RenderDialog.cpp
diff --git a/Source/WebCore/rendering/RenderDialog.cpp b/Source/WebCore/rendering/RenderDialog.cpp
index b8f3d198574f083664500983f180aa2d93850e9d..f40abc688ff32a499ef4c5b15c9222a81b31c97b 100644
--- a/Source/WebCore/rendering/RenderDialog.cpp
+++ b/Source/WebCore/rendering/RenderDialog.cpp
@@ -40,28 +40,37 @@ void RenderDialog::layout()
     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();
 }