if (mSelection) mSelection->ResetSelection(this, mRootFrame);
PresShell::ContentChanged(nsIDocument *aDocument,                          nsIContent*  aContent,                          nsISupports* aSubContent){  NS_PRECONDITION(nsnull != mRootFrame, "null root frame");  EnterReflowLock();  nsresult rv = mStyleSet->ContentChanged(mPresContext, aContent, aSubContent);  ExitReflowLock();  return rv;}