Removed StartProvisionalNavigationExitedWithEmptyNavigationManager metric.

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 <WebKit/WebKit.h>
 
 #import <objc/runtime.h>
 #include <stddef.h>
@@ skipping 4576 matching lines @@
         [self abortLoad];
         NavigationManager::WebLoadParams params(webViewURL);
         [self loadWithParams:params];
       }
       return;
     } else {
       [self registerLoadRequest:webViewURL];
     }
   }
 
-  if (![self currentSessionEntry]) {
-    // In this state CRWWebController will crash in |didCommitNavigation:|
-    // (crbug.com/676458). It's unclear if web controller could get into this
-    // state but it's one of the guesses for crbug.com/676458 root cause. Report
-    // UMA historgam if that happens.
-    // TODO(crbug.com/677552): Remove this historgam.
-    UMA_HISTOGRAM_BOOLEAN(
-        "WebController."
-        "StartProvisionalNavigationExitedWithEmptyNavigationManager",
-        true);
-  }
-
   // Ensure the URL is registered and loadPhase is as expected.
   DCHECK(_lastRegisteredRequestURL == webViewURL);
   DCHECK(self.loadPhase == web::LOAD_REQUESTED);
 }
 
 - (void)webView:(WKWebView*)webView
     didReceiveServerRedirectForProvisionalNavigation:(WKNavigation*)navigation {
   [_navigationStates setState:web::WKNavigationState::REDIRECTED
                 forNavigation:navigation];
 
@@ skipping 620 matching lines @@
 - (void)simulateLoadRequestWithURL:(const GURL&)URL {
   _lastRegisteredRequestURL = URL;
   _loadPhase = web::LOAD_REQUESTED;
 }
 
 - (NSString*)referrerFromNavigationAction:(WKNavigationAction*)action {
   return [action.request valueForHTTPHeaderField:kReferrerHeaderName];
 }
 
 @end