Update SupportsUserData uses with unique_ptr.

components/pdf/browser/pdf_web_contents_helper.h

Index: components/pdf/browser/pdf_web_contents_helper.h
diff --git a/components/pdf/browser/pdf_web_contents_helper.h b/components/pdf/browser/pdf_web_contents_helper.h
index 080dca40599dd9e75f31b3a35d83f4e32fedef24..0d848c7bfc582895437ca8652f8f6d550b24d437 100644
--- a/components/pdf/browser/pdf_web_contents_helper.h
+++ b/components/pdf/browser/pdf_web_contents_helper.h
@@ -29,6 +29,8 @@ class PDFWebContentsHelper
       public content::WebContentsUserData<PDFWebContentsHelper>,
       public mojom::PdfService {
  public:
+  ~PDFWebContentsHelper() override;
+
   static void CreateForWebContentsWithClient(
       content::WebContents* contents,
       std::unique_ptr<PDFWebContentsHelperClient> client);
@@ -36,7 +38,6 @@ class PDFWebContentsHelper
  private:
   PDFWebContentsHelper(content::WebContents* web_contents,
                        std::unique_ptr<PDFWebContentsHelperClient> client);
-  ~PDFWebContentsHelper() override;
 
   // mojom::PdfService:
   void HasUnsupportedFeature() override;