Coalesce event router Init calls into their constructors.

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

Index: chrome/browser/extensions/api/web_navigation/web_navigation_api.cc
diff --git a/chrome/browser/extensions/api/web_navigation/web_navigation_api.cc b/chrome/browser/extensions/api/web_navigation/web_navigation_api.cc
index 5e3f1adc3c4a76a4061f1bafdb69518de06cf43e..7cb61a3995f9c9a5d2925a9bd3f2f6d05b3dcffc 100644
--- a/chrome/browser/extensions/api/web_navigation/web_navigation_api.cc
+++ b/chrome/browser/extensions/api/web_navigation/web_navigation_api.cc
@@ -73,15 +73,8 @@ WebNavigationEventRouter::PendingWebContents::PendingWebContents(
 WebNavigationEventRouter::PendingWebContents::~PendingWebContents() {}
 
 WebNavigationEventRouter::WebNavigationEventRouter(Profile* profile)
-    : profile_(profile) {}
-
-WebNavigationEventRouter::~WebNavigationEventRouter() {
-  BrowserList::RemoveObserver(this);
-}
-
-void WebNavigationEventRouter::Init() {
-  if (!registrar_.IsEmpty())
-    return;
+    : profile_(profile) {
+  CHECK(registrar_.IsEmpty());
   registrar_.Add(this,
                  chrome::NOTIFICATION_RETARGETING,
                  content::NotificationService::AllSources());
@@ -99,6 +92,10 @@ void WebNavigationEventRouter::Init() {
   }
 }
 
+WebNavigationEventRouter::~WebNavigationEventRouter() {
+  BrowserList::RemoveObserver(this);
+}
+
 void WebNavigationEventRouter::OnBrowserAdded(Browser* browser) {
   if (!profile_->IsSameProfile(browser->profile()))
     return;