Allow using a BrowserViewController without BookmarkModel for testing.

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 923 matching lines @@
 
 - (instancetype)initWithCoder:(NSCoder*)aDecoder {
   NOTREACHED();
   return nil;
 }
 
 - (void)dealloc {
   _tabStripController.reset();
   _infoBarContainer.reset();
   _readingListMenuNotifier.reset();
-  _bookmarkModel->RemoveObserver(_bookmarkModelBridge.get());
+  if (_bookmarkModel)
+    _bookmarkModel->RemoveObserver(_bookmarkModelBridge.get());
   [_model removeObserver:self];
   [[UpgradeCenter sharedInstance] unregisterClient:self];
   [[NSNotificationCenter defaultCenter] removeObserver:self];
   [_toolbarController setDelegate:nil];
   if (_voiceSearchController.get())
     _voiceSearchController->SetDelegate(nil);
   [_rateThisAppDialog setDelegate:nil];
   [_model closeAllTabs];
   [super dealloc];
 }
@@ skipping 694 matching lines @@
   }
   NSUInteger count = [_model count];
   for (NSUInteger index = 0; index < count; ++index)
     [self installDelegatesForTab:[_model tabAtIndex:index]];
 
   [self registerForNotifications];
 
   _imageFetcher->SetRequestContextGetter(_browserState->GetRequestContext());
   _dominantColorCache.reset([[NSMutableDictionary alloc] init]);
 
-  // Register for bookmark changed notification.
-  _bookmarkModelBridge.reset(new BrowserBookmarkModelBridge(self));
+  // Register for bookmark changed notification (BookmarkModel may be null
+  // during testing, so explicitly support this).
   _bookmarkModel = ios::BookmarkModelFactory::GetForBrowserState(_browserState);
-  _bookmarkModel->AddObserver(_bookmarkModelBridge.get());
+  if (_bookmarkModel) {
+    _bookmarkModelBridge.reset(new BrowserBookmarkModelBridge(self));
+    _bookmarkModel->AddObserver(_bookmarkModelBridge.get());
+  }
 }
 
 - (void)ensureViewCreated {
   ignore_result([self view]);
 }
 
 - (void)browserStateDestroyed {
   [self setActive:NO];
   // Reset the toolbar opacity in case it was changed for contextual search.
   [self updateToolbarControlsAlpha:1.0];
@@ skipping 475 matching lines @@
   }
 }
 
 #pragma mark - External files
 
 - (NSSet*)referencedExternalFiles {
   NSSet* filesReferencedByTabs = [_model currentlyReferencedExternalFiles];
 
   // TODO(noyau): this is incorrect, the caller should know that the model is
   // not loaded yet.
-  if (!_bookmarkModel->loaded())
+  if (!_bookmarkModel || !_bookmarkModel->loaded())
     return filesReferencedByTabs;
 
   std::vector<bookmarks::BookmarkModel::URLAndTitle> bookmarks;
   _bookmarkModel->GetBookmarks(&bookmarks);
   NSMutableSet* bookmarkedFiles = [NSMutableSet set];
   for (const auto& bookmark : bookmarks) {
     GURL bookmarkUrl = bookmark.url;
     if (UrlIsExternalFileReference(bookmarkUrl)) {
       [bookmarkedFiles
           addObject:base::SysUTF8ToNSString(bookmarkUrl.ExtractFileName())];
@@ skipping 2968 matching lines @@
 
 - (UIView*)voiceSearchButton {
   return _voiceSearchButton;
 }
 
 - (id<LogoAnimationControllerOwner>)logoAnimationControllerOwner {
   return [self currentLogoAnimationControllerOwner];
 }
 
 @end