message: scrolling works with line breaks supplying y coord
diff: @@ -1928,6 +1928,7 @@ function makeFontInfo(docContext: IDocumentContext): Paragraph.IFontInfo {
  }
  export interface IFlowBreakInfo extends Paragraph.IBreakInfo {
  + lineY?: number;
  lineX?: number;
  lineWidth?: number;
  lineHeight?: number;
  @@ -1965,6 +1966,7 @@ export function breakPGIntoLinesFFVP(itemInfo: Paragraph.IParagraphItemInfo, def
  }
  if ((committedItemsWidth + item.width) > lineWidth) {
  checkViewportFirstLine(blockRunPos);
  + prevBreak.lineY = viewport.getLineTop();
  prevBreak.lineX = viewport.getLineX();
  prevBreak.lineHeight = committedItemsHeight;
  prevBreak = { lineWidth, posInPG: blockRunPos, startItemIndex: i };
  @@ -1977,6 +1979,7 @@ export function breakPGIntoLinesFFVP(itemInfo: Paragraph.IParagraphItemInfo, def
  posInPG += item.text.length;
  if (committedItemsWidth > lineWidth) {
  checkViewportFirstLine(posInPG);
  + prevBreak.lineY = viewport.getLineTop();
  prevBreak.lineX = viewport.getLineX();
  prevBreak.lineHeight = committedItemsHeight;
  prevBreak = { lineWidth, posInPG, startItemIndex: i };
  @@ -2002,6 +2005,8 @@ export function breakPGIntoLinesFFVP(itemInfo: Paragraph.IParagraphItemInfo, def
  committedItemsHeight = Math.max(committedItemsHeight,
  item.height ? item.height : defaultLineHeight);
  }
  + checkViewportFirstLine(posInPG);
  + prevBreak.lineY=viewport.getLineTop();
  prevBreak.lineX = viewport.getLineX();
  prevBreak.lineHeight = committedItemsHeight;
  viewport.setLineTop(savedTop);
  @@ -2088,6 +2093,7 @@ function renderFlow(layoutContext: ILayoutContext, targetTranslation: string, de
  lineWidth = breakInfo.lineWidth;
  lineHeight = breakInfo.lineHeight;
  lineX = breakInfo.lineX;
  + lineY = breakInfo.lineY;
  }
  let indentWidth = 0;
  let contentWidth = lineWidth;
  