Bug 430389: Use correct clip-rect to prevent multipage print-selection output...

  // Make sure we don't draw where we aren't supposed to draw, especially

  // when printing selection

  nsRect clipRect(nsPoint(0, 0), pageContentFrame->GetSize());

  // Note: this computation matches how we compute maxSize.height

  // in nsPageFrame::Reflow

  nscoord expectedPageContentHeight = 

    NSToCoordCeil((GetSize().height - mPD->mReflowMargin.TopBottom()) / scale);

  if (clipRect.height > expectedPageContentHeight) {

    // We're doing print-selection, with one long page-content frame.

    // Clip to the appropriate page-content slice for the current page.

    NS_ASSERTION(mPageNum > 0, "page num should be positive");

    clipRect.y =  expectedPageContentHeight * (mPageNum - 1);

    clipRect.height = expectedPageContentHeight;

    NS_ASSERTION(clipRect.y < pageContentFrame->GetSize().height,

                 "Should be clipping to region inside the page content bounds");

  }

  aRenderingContext.SetClipRect(clipRect, nsClipCombine_kIntersect);

  const nsStyleBorder* border = GetStyleBorder();