Replace ScopedObserver with base::ScopedObservation in /content/browser/renderer_host/.

ScopedObserver is being deprecated in favor of two new classes:
- base::ScopedObservation for observers that only ever observe
  a single source.
- base::ScopedMultiSourceObservation for observers that do or may
  observe more than a single source.
This CL was uploaded by git cl split.

R=tapted@chromium.org

Bug: 1145565
Change-Id: Ic8f6127259269507bb4c44bdb4abd8371da08ab0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2526961
Commit-Queue: Avi Drissman <avi@chromium.org>
Reviewed-by: Avi Drissman <avi@chromium.org>
Auto-Submit: Sigurður Ásgeirsson <siggi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#825974}

content/browser/renderer_host/popup_menu_helper_mac.h

@@ -11,7 +11,7 @@
 #include "base/compiler_specific.h"
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
-#include "base/scoped_observer.h"
+#include "base/scoped_observation.h"
 #include "content/common/content_export.h"
 #include "content/public/browser/render_widget_host.h"
 #include "content/public/browser/render_widget_host_observer.h"
@@ -77,7 +77,8 @@ class PopupMenuHelper : public RenderWidgetHostObserver {
 
   Delegate* delegate_;  // Weak. Owns |this|.
 
-  ScopedObserver<RenderWidgetHost, RenderWidgetHostObserver> observer_{this};
+  base::ScopedObservation<RenderWidgetHost, RenderWidgetHostObserver>
+      observation_{this};
   base::WeakPtr<RenderFrameHostImpl> render_frame_host_;
   mojo::Remote<blink::mojom::PopupMenuClient> popup_client_;
   WebMenuRunner* menu_runner_ = nil;

content/browser/renderer_host/popup_menu_helper_mac.mm

@@ -35,7 +35,7 @@ PopupMenuHelper::PopupMenuHelper(
       popup_client_(std::move(popup_client)) {
   RenderWidgetHost* widget_host =
       render_frame_host->GetRenderViewHost()->GetWidget();
-  observer_.Add(widget_host);
+  observation_.Observe(widget_host);
 
   popup_client_.set_disconnect_handler(
       base::BindOnce(&PopupMenuHelper::Hide, weak_ptr_factory_.GetWeakPtr()));
@@ -159,7 +159,8 @@ void PopupMenuHelper::RenderWidgetHostVisibilityChanged(
 }
 
 void PopupMenuHelper::RenderWidgetHostDestroyed(RenderWidgetHost* widget_host) {
-  observer_.Remove(widget_host);
+  DCHECK(observation_.IsObservingSource(widget_host));
+  observation_.RemoveObservation();
 }
 
 }  // namespace content