Retire ScopedObserver in /components/translate.

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=anthonyvd@chromium.org

Bug: 1145565
Change-Id: Ic75c0df148d4ef69da3675276ad5728dd6dcf864
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2532960
Auto-Submit: Sigurður Ásgeirsson <siggi@chromium.org>
Reviewed-by: anthonyvd <anthonyvd@chromium.org>
Commit-Queue: Sigurður Ásgeirsson <siggi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#826443}

components/translate/content/browser/translate_waiter.cc

@@ -9,7 +9,7 @@ namespace translate {
 TranslateWaiter::TranslateWaiter(ContentTranslateDriver* translate_driver,
                                  WaitEvent wait_event)
     : wait_event_(wait_event) {
-  scoped_observer_.Add(translate_driver);
+  scoped_observation_.Observe(translate_driver);
 }
 
 TranslateWaiter::~TranslateWaiter() = default;

components/translate/content/browser/translate_waiter.h

@@ -9,7 +9,7 @@
 
 #include "base/macros.h"
 #include "base/run_loop.h"
-#include "base/scoped_observer.h"
+#include "base/scoped_observation.h"
 #include "components/translate/content/browser/content_translate_driver.h"
 #include "components/translate/core/common/translate_errors.h"
 
@@ -42,8 +42,9 @@ class TranslateWaiter : ContentTranslateDriver::Observer {
 
  private:
   WaitEvent wait_event_;
-  ScopedObserver<ContentTranslateDriver, ContentTranslateDriver::Observer>
-      scoped_observer_{this};
+  base::ScopedObservation<ContentTranslateDriver,
+                          ContentTranslateDriver::Observer>
+      scoped_observation_{this};
   base::RunLoop run_loop_;
 
   DISALLOW_COPY_AND_ASSIGN(TranslateWaiter);