Switch SupportsUserData uses to use unique_ptr.

chrome/browser/task_manager/providers/web_contents/background_contents_tag.h

Index: chrome/browser/task_manager/providers/web_contents/background_contents_tag.h
diff --git a/chrome/browser/task_manager/providers/web_contents/background_contents_tag.h b/chrome/browser/task_manager/providers/web_contents/background_contents_tag.h
index 33b3990d02b6cda5b30253dbe609e32eb059cc21..e05ad02a2b0609ed3d97c7157071123d29c472c8 100644
--- a/chrome/browser/task_manager/providers/web_contents/background_contents_tag.h
+++ b/chrome/browser/task_manager/providers/web_contents/background_contents_tag.h
@@ -17,6 +17,8 @@ namespace task_manager {
 // service.
 class BackgroundContentsTag : public WebContentsTag {
  public:
+  ~BackgroundContentsTag() override;
+
   // task_manager::WebContentsTag:
   BackgroundContentsTask* CreateTask() const override;
 
@@ -25,7 +27,6 @@ class BackgroundContentsTag : public WebContentsTag {
 
   BackgroundContentsTag(content::WebContents* web_contents,
                         BackgroundContents* background_contents);
-  ~BackgroundContentsTag() override;
 
   // The owning BackgroundContents.
   BackgroundContents* background_contents_;