[ios] Added web// public API to let embedder observe loading progress.

ios/web/web_state/ui/crw_web_controller.mm

 // Copyright 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #import "ios/web/web_state/ui/crw_web_controller.h"
 
 #import <objc/runtime.h>
 #include <stddef.h>
 
 #include <cmath>
@@ skipping 4938 matching lines @@
                       ofObject:(id)object
                         change:(NSDictionary*)change
                        context:(void*)context {
   NSString* dispatcherSelectorName = self.WKWebViewObservers[keyPath];
   DCHECK(dispatcherSelectorName);
   if (dispatcherSelectorName)
     [self performSelector:NSSelectorFromString(dispatcherSelectorName)];
 }
 
 - (void)webViewEstimatedProgressDidChange {
-  if ([self.delegate
+  if ([self isBeingDestroyed])
+    return;
+
+  self.webStateImpl->SendChangeLoadProgress([_webView estimatedProgress]);
+  if ([_delegate
           respondsToSelector:@selector(webController:didUpdateProgress:)]) {
-    [self.delegate webController:self
-               didUpdateProgress:[self.webView estimatedProgress]];
+    [_delegate webController:self
+           didUpdateProgress:[_webView estimatedProgress]];
   }
 }
 
 - (void)webViewSecurityFeaturesDidChange {
   if (self.loadPhase == web::LOAD_REQUESTED) {
     // Do not update SSL Status for pending load. It will be updated in
     // |webView:didCommitNavigation:| callback.
     return;
   }
   [self updateSSLStatusForCurrentNavigationItem];
@@ skipping 285 matching lines @@
   }
 
   return web::WEB_VIEW_DOCUMENT_TYPE_GENERIC;
 }
 
 - (NSString*)refererFromNavigationAction:(WKNavigationAction*)action {
   return [action.request valueForHTTPHeaderField:@"Referer"];
 }
 
 @end