Check if WebContents::IsBeingDestroyed when it comes to the foreground.

Seems to be possible on shutdown. For more context see attached bug.

Also switched scoped_observ{er->ation} because we always observe a
single source (no functional change here).

Bug: 1167491
Change-Id: I675f0bc57abe7067960500a7e6607be3f7b8d36f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2631979Reviewed-by: Dominick Ng <dominickn@chromium.org>
Commit-Queue: Glen Robertson <glenrob@chromium.org>
Cr-Commit-Position: refs/heads/master@{#844451}

chrome/browser/ui/web_applications/web_app_metrics.cc

@@ -379,14 +379,18 @@ void WebAppMetrics::UpdateUkmData(WebContents* web_contents,
 void WebAppMetrics::UpdateForegroundWebContents(WebContents* web_contents) {
   if (web_contents == foreground_web_contents_)
     return;
-  app_banner_manager_observer_.RemoveAll();
+  if (web_contents && web_contents->IsBeingDestroyed()) {
+    base::debug::DumpWithoutCrashing();
+    web_contents = nullptr;
+  }
+  app_banner_manager_observer_.Reset();
   foreground_web_contents_ = web_contents;
   WebContentsObserver::Observe(web_contents);
   if (web_contents) {
     auto* app_banner_manager =
         webapps::AppBannerManager::FromWebContents(web_contents);
     DCHECK(app_banner_manager);
-    app_banner_manager_observer_.Add(app_banner_manager);
+    app_banner_manager_observer_.Observe(app_banner_manager);
   }
 }
 

chrome/browser/ui/web_applications/web_app_metrics.h

@@ -7,7 +7,7 @@
 
 #include "base/memory/weak_ptr.h"
 #include "base/power_monitor/power_observer.h"
-#include "base/scoped_observer.h"
+#include "base/scoped_observation.h"
 #include "chrome/browser/banners/app_banner_manager.h"
 #include "chrome/browser/ui/browser_tab_strip_tracker.h"
 #include "chrome/browser/ui/tabs/tab_strip_model_observer.h"
@@ -96,7 +96,8 @@ class WebAppMetrics : public KeyedService,
   Profile* const profile_;
 
   BrowserTabStripTracker browser_tab_strip_tracker_;
-  ScopedObserver<webapps::AppBannerManager, webapps::AppBannerManager::Observer>
+  base::ScopedObservation<webapps::AppBannerManager,
+                          webapps::AppBannerManager::Observer>
       app_banner_manager_observer_{this};
 
   base::WeakPtrFactory<WebAppMetrics> weak_ptr_factory_{this};