Make down-conversion explicit from CFX_Widetring to CFX_WideStringC.

xfa/fxfa/app/xfa_textlayout.h

Index: xfa/fxfa/app/xfa_textlayout.h
diff --git a/xfa/fxfa/app/xfa_textlayout.h b/xfa/fxfa/app/xfa_textlayout.h
index 9b92e1796a2ff476b7d7c8671d4ed2793002bbc2..d92a2f40586485e02a345c9fc2b1cf0ada913491 100644
--- a/xfa/fxfa/app/xfa_textlayout.h
+++ b/xfa/fxfa/app/xfa_textlayout.h
@@ -25,7 +25,9 @@ class CXFA_CSSTagProvider : public IFDE_CSSTagProvider {
  public:
   CXFA_CSSTagProvider() : m_bTagAviliable(FALSE), m_bContent(FALSE) {}
   virtual ~CXFA_CSSTagProvider();
-  virtual CFX_WideStringC GetTagName() { return m_wsTagName; }
+
+  // Note: |this| must outlive the use of GetTagName()'s result.
+  virtual CFX_WideStringC GetTagName() { return m_wsTagName.AsWideStringC(); }
   virtual FX_POSITION GetFirstAttribute() {
     return m_Attributes.GetStartPosition();
   }