Added |load_completion_status| to WebStateObserver's |PageLoaded|.

This CL also introduces the web::PageLoadCompletionStatus enum.
This was done to support future WebStateObserver subclasses that
require notifications of failed page loads.

BUG=none

Review URL: https://codereview.chromium.org/835203002

Cr-Commit-Position: refs/heads/master@{#310188}

components/translate/ios/browser/language_detection_controller.h

@@ -76,7 +76,8 @@ class LanguageDetectionController : public web::WebStateObserver {
                        const base::string16& text);
 
   // web::WebStateObserver implementation:
-  void PageLoaded() override;
+  void PageLoaded(
+      web::PageLoadCompletionStatus load_completion_status) override;
   void URLHashChanged() override;
   void HistoryStateChanged() override;
   void WebStateDestroyed() override;

components/translate/ios/browser/language_detection_controller.mm

@@ -127,8 +127,10 @@ void LanguageDetectionController::OnTextRetrieved(
 
 // web::WebStateObserver implementation:
 
-void LanguageDetectionController::PageLoaded() {
-  StartLanguageDetection();
+void LanguageDetectionController::PageLoaded(
+    web::PageLoadCompletionStatus load_completion_status) {
+  if (load_completion_status == web::PageLoadCompletionStatus::SUCCESS)
+    StartLanguageDetection();
 }
 
 void LanguageDetectionController::URLHashChanged() {

ios/web/public/web_state/web_state_observer.h

@@ -13,6 +13,8 @@ struct LoadCommittedDetails;
 class WebState;
 class WebStateImpl;
 
+enum class PageLoadCompletionStatus : bool { SUCCESS = 0, FAILURE = 1 };
+
 // An observer API implemented by classes which are interested in various page
 // load events from WebState.
 class WebStateObserver {
@@ -28,7 +30,7 @@ class WebStateObserver {
       const LoadCommittedDetails& load_details) {}
 
   // Called when the current page is loaded.
-  virtual void PageLoaded() {}
+  virtual void PageLoaded(PageLoadCompletionStatus load_completion_status) {}
 
   // Called on URL hash change events.
   virtual void URLHashChanged() {}