Switch SupportsUserData uses to use unique_ptr.

chrome/browser/android/download/chrome_download_delegate.h

Index: chrome/browser/android/download/chrome_download_delegate.h
diff --git a/chrome/browser/android/download/chrome_download_delegate.h b/chrome/browser/android/download/chrome_download_delegate.h
index 9e0347b5b22610a727f1d1bdc63ef3e3f012ae48..d1a6e69d6ce880cca84f035a4e4e72cf09c4f3ec 100644
--- a/chrome/browser/android/download/chrome_download_delegate.h
+++ b/chrome/browser/android/download/chrome_download_delegate.h
@@ -11,6 +11,8 @@
 class ChromeDownloadDelegate
     : public content::WebContentsUserData<ChromeDownloadDelegate> {
  public:
+  ~ChromeDownloadDelegate() override;
+
   // Returns true iff this request resulted in the tab creating the download
   // to close.
   static bool EnqueueDownloadManagerRequest(jobject chrome_download_delegate,
@@ -33,7 +35,6 @@ class ChromeDownloadDelegate
  private:
   explicit ChromeDownloadDelegate(content::WebContents* contents);
   friend class content::WebContentsUserData<ChromeDownloadDelegate>;
-  ~ChromeDownloadDelegate() override;
 
   // A reference to the Java ChromeDownloadDelegate object.
   jobject java_ref_;