Switch SupportsUserData uses to use unique_ptr.

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

Index: chrome/browser/task_manager/providers/web_contents/guest_tag.h
diff --git a/chrome/browser/task_manager/providers/web_contents/guest_tag.h b/chrome/browser/task_manager/providers/web_contents/guest_tag.h
index 725a32716337904bee15b8ae625286a674c85aed..14048dee40924e107bc464ed8824f2e9da18c9ea 100644
--- a/chrome/browser/task_manager/providers/web_contents/guest_tag.h
+++ b/chrome/browser/task_manager/providers/web_contents/guest_tag.h
@@ -15,6 +15,8 @@ namespace task_manager {
 // which represents browser <*view> tag plugin guests.
 class GuestTag : public WebContentsTag {
  public:
+  ~GuestTag() override;
+
   // task_manager::WebContentsTag:
   GuestTask* CreateTask() const override;
 
@@ -22,7 +24,6 @@ class GuestTag : public WebContentsTag {
   friend class WebContentsTags;
 
   explicit GuestTag(content::WebContents* web_contents);
-  ~GuestTag() override;
 
   DISALLOW_COPY_AND_ASSIGN(GuestTag);
 };