Replace a DCHECK in BVC with an early return.

ios/chrome/browser/ui/browser_view_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/chrome/browser/ui/browser_view_controller.h"
 
 #import <AssetsLibrary/AssetsLibrary.h>
 #import <MobileCoreServices/MobileCoreServices.h>
 #import <PassKit/PassKit.h>
 #import <Photos/Photos.h>
@@ skipping 4386 matching lines @@
   __weak BrowserViewController* weakSelf = self;
   Tab* currentTab = [_model currentTab];
   if (currentTab) {
     FindTabHelper::FromWebState(currentTab.webState)->StopFinding(^{
       [weakSelf updateFindBar:NO shouldFocus:NO];
     });
   }
 }
 
 - (void)updateFindBar:(BOOL)initialUpdate shouldFocus:(BOOL)shouldFocus {
-  DCHECK([_model currentTab]);
+  if (![_model currentTab]) {

[rohitrao (ping after 24h), 2017/06/20 14:02:44]

Consider adding a link to the crbug and explaining why this early return exists.

[stkhapugin, 2017/06/20 14:09:42]

Done.

+    return;
+  }
   auto* helper = FindTabHelper::FromWebState([_model currentTab].webState);
   if (helper && helper->IsFindUIActive()) {
     if (initialUpdate && !_isOffTheRecord) {
       helper->RestoreSearchTerm();
     }
 
     [self setFramesForHeaders:[self headerViews]
                      atOffset:[self currentHeaderOffset]];
     [_findBarController updateView:helper->GetFindResult()
                      initialUpdate:initialUpdate
@@ skipping 822 matching lines @@
 
 - (UIView*)voiceSearchButton {
   return _voiceSearchButton;
 }
 
 - (id<LogoAnimationControllerOwner>)logoAnimationControllerOwner {
   return [self currentLogoAnimationControllerOwner];
 }
 
 @end