Backing out bug 397510 again because again it looks like it might have caused...

  void SetAtStartOfLine() {

    mStartOfLine = PR_TRUE;

    mCanStopOnThisLine = PR_FALSE;

  }

  void SetSkipIncompleteTextRuns(PRBool aSkip) {

    mSkipIncompleteTextRuns = aSkip;

  void SetCommonAncestorWithLastFrame(nsIFrame* aFrame) {

    mCommonAncestorWithLastFrame = aFrame;

  }

  PRBool CanStopOnThisLine() {

    return mCanStopOnThisLine;

  }

  nsIFrame* GetCommonAncestorWithLastFrame() {

    return mCommonAncestorWithLastFrame;

  }

    mMaxTextLength = 0;

    mDoubleByteText = PR_FALSE;

  }

  void ResetLineBreaker() {

    mLineBreaker.Reset();

  }

  void AccumulateRunInfo(nsTextFrame* aFrame);

  void BuildTextRunForFrames(void* aTextBuffer);

  void AssignTextRun(gfxTextRun* aTextRun);

  PRPackedBool                  mTrimNextRunLeadingWhitespace;

  PRPackedBool                  mCurrentRunTrimLeadingWhitespace;

  PRPackedBool                  mSkipIncompleteTextRuns;

  PRPackedBool                  mCanStopOnThisLine;

};

static nsIFrame*

  return FB_CONTINUE;

}

// build text runs for the 50 lines following aForFrame, and stop after that

// when we get a chance.

#define NUM_LINES_TO_BUILD_TEXT_RUNS 50

/**

 * General routine for building text runs. This is hairy because of the need

 * to build text runs that span content nodes.

  }

  // Find the line containing aForFrame

  nsBlockFrame::line_iterator startLine;

  nsBlockFrame::line_iterator line;

  if (aForFrameLine) {

    startLine = *aForFrameLine;

    line = *aForFrameLine;

  } else {

    NS_ASSERTION(aForFrame, "One of aForFrame or aForFrameLine must be set!");

    nsIFrame* immediateChild =

        nsLayoutUtils::FindChildContainingDescendant(block,

          presContext->FrameManager()->GetPlaceholderFrameFor(immediateChild));

    }

    startLine = block->FindLineFor(immediateChild);

    NS_ASSERTION(startLine != block->end_lines(),

    line = block->FindLineFor(immediateChild);

    NS_ASSERTION(line != block->end_lines(),

                 "Frame is not in the block!!!");

  }

  // but we discard them instead of assigning them to frames.

  // This is a little awkward because we traverse lines in the reverse direction

  // but we traverse the frames in each line in the forward direction.

  nsBlockInFlowLineIterator backIterator(block, startLine, PR_FALSE);

  nsBlockInFlowLineIterator backIterator(block, line, PR_FALSE);

  nsTextFrame* stopAtFrame = aForFrame;

  nsTextFrame* nextLineFirstTextFrame = nsnull;

  PRBool seenTextRunBoundaryOnLaterLine = PR_FALSE;

  PRBool mayBeginInTextRun = PR_TRUE;

  PRBool inOverflow = PR_FALSE;

  nsBlockFrame::line_iterator line;

  while (PR_TRUE) {

    line = backIterator.GetLine();

    block = backIterator.GetContainer();

  // text run boundary is required we flush textRunFrames ((re)building their

  // gfxTextRuns as necessary).

  nsBlockInFlowLineIterator forwardIterator(block, line, inOverflow);

  PRBool seenStartLine = PR_FALSE;

  PRUint32 linesAfterStartLine = 0;

  do {

    line = forwardIterator.GetLine();

    if (line->IsBlock())

      scanner.ScanFrame(child);

      child = child->GetNextSibling();

    }

    if (line == startLine) {

      seenStartLine = PR_TRUE;

    }

    if (seenStartLine) {

      ++linesAfterStartLine;

      if (linesAfterStartLine >= NUM_LINES_TO_BUILD_TEXT_RUNS && scanner.CanStopOnThisLine()) {

        // Don't flush; we may be in the middle of a textrun that we can't

        // end here. That's OK, we just won't build it.

        // Note that we must already have finished the textrun for aForFrame,

        // because we've seen the end of a textrun in a line after the line

        // containing aForFrame.

        scanner.ResetLineBreaker();

        return;

      }

    }

  } while (forwardIterator.Next());

  // Set mStartOfLine so FlushFrames knows its textrun ends a line

    mBreakSinks.Clear();

  }

  mCanStopOnThisLine = PR_TRUE;

  ResetRunInfo();

}