Make ~WebNavigationEventRouter remove itself from browsers

I don't think this is related to the crash I'm seeing, but I noticed
it when looking for dangling TabStripModelObservers.

BUG=286162
TEST=none
R=yoz@chromium.org

Review URL: https://chromiumcodereview.appspot.com/23547006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@221959 0039d316-1c4b-4281-b951-d872f2087c98

chrome/browser/extensions/api/web_navigation/web_navigation_api.cc

@@ -91,12 +91,13 @@ WebNavigationEventRouter::WebNavigationEventRouter(Profile* profile)
                  content::NotificationService::AllSources());
 
   BrowserList::AddObserver(this);
-  for (chrome::BrowserIterator it; !it.done(); it.Next()) {
+  for (chrome::BrowserIterator it; !it.done(); it.Next())
     OnBrowserAdded(*it);
-  }
 }
 
 WebNavigationEventRouter::~WebNavigationEventRouter() {
+  for (chrome::BrowserIterator it; !it.done(); it.Next())
+    OnBrowserRemoved(*it);
   BrowserList::RemoveObserver(this);
 }