Remove RenderViewObserverTracer

It has been used in 4 years since https://crrev.com/cb959ce66a
so I don't think anyone is going to use it now.

BUG=1097816

Change-Id: I492413144ca1d7905657fe3717ff8cd9c7a5f37c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2476755Reviewed-by: Avi Drissman <avi@chromium.org>
Commit-Queue: Dave Tapuska <dtapuska@chromium.org>
Cr-Commit-Position: refs/heads/master@{#817675}

content/public/renderer/BUILD.gn

@@ -49,7 +49,6 @@ target(link_target_type, "renderer_sources") {
     "render_view.h",
     "render_view_observer.cc",
     "render_view_observer.h",
-    "render_view_observer_tracker.h",
     "render_view_visitor.h",
     "renderer_ppapi_host.h",
     "request_peer.h",

content/public/renderer/render_view_observer_tracker.h

-// Copyright (c) 2012 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-// Helper class used to find the RenderViewObservers for a given RenderView.
-//
-// Example usage:
-//
-//   class MyRVO : public RenderViewObserver,
-//                 public RenderViewObserverTracker<MyRVO> {
-//     ...
-//   };
-//
-//   MyRVO::MyRVO(RenderView* render_view)
-//       : RenderViewObserver(render_view),
-//         RenderViewObserverTracker<MyRVO>(render_view) {
-//     ...
-//   }
-//
-//  void SomeFunction(RenderView* rv) {
-//    MyRVO* my_rvo = new MyRVO(rv);
-//    MyRVO* my_rvo_tracked = MyRVO::Get(rv);
-//    // my_rvo == my_rvo_tracked
-//  }
-
-#ifndef CONTENT_PUBLIC_RENDERER_RENDER_VIEW_OBSERVER_TRACKER_H_
-#define CONTENT_PUBLIC_RENDERER_RENDER_VIEW_OBSERVER_TRACKER_H_
-
-#include <map>
-
-#include "base/lazy_instance.h"
-#include "base/macros.h"
-
-namespace content {
-
-class RenderView;
-
-template <class T>
-class RenderViewObserverTracker {
- public:
-  static T* Get(const RenderView* render_view) {
-    return static_cast<T*>(render_view_map_.Get()[render_view]);
-  }
-
-  explicit RenderViewObserverTracker(const RenderView* render_view)
-      : render_view_(render_view) {
-    render_view_map_.Get()[render_view] = this;
-  }
-  ~RenderViewObserverTracker() {
-    render_view_map_.Get().erase(render_view_);
-  }
-
- private:
-  const RenderView* render_view_;
-
-  static typename base::LazyInstance<
-      std::map<const RenderView*, RenderViewObserverTracker<T>*>>::
-      DestructorAtExit render_view_map_;
-
-  DISALLOW_COPY_AND_ASSIGN(RenderViewObserverTracker<T>);
-};
-
-template <class T>
-typename base::LazyInstance<
-    std::map<const RenderView*, RenderViewObserverTracker<T>*>>::
-    DestructorAtExit RenderViewObserverTracker<T>::render_view_map_ =
-        LAZY_INSTANCE_INITIALIZER;
-
-}  // namespace content
-
-#endif  // CONTENT_PUBLIC_RENDERER_RENDER_VIEW_OBSERVER_TRACKER_H_