Clean up defensive TabManager handling

chrome/browser/memory/tab_manager_observer_browsertest.cc

 // Copyright (c) 2016 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.
 
 #include "base/macros.h"
 #include "chrome/browser/browser_process.h"
 #include "chrome/browser/memory/tab_manager.h"
 #include "chrome/browser/memory/tab_manager_observer.h"
 #include "chrome/browser/memory/tab_manager_web_contents_data.h"
 #include "chrome/browser/ui/browser.h"
@@ skipping 65 matching lines @@
   int nb_events_;
   WebContents* contents_;
   bool is_discarded_;
   bool is_auto_discardable_;
 
   DISALLOW_COPY_AND_ASSIGN(MockTabManagerObserver);
 };
 
 IN_PROC_BROWSER_TEST_F(TabManagerObserverTest, OnDiscardStateChange) {
   TabManager* tab_manager = g_browser_process->GetTabManager();
-  ASSERT_TRUE(tab_manager);
   auto* tsm = browser()->tab_strip_model();
   set_tab_strip_model(tsm);
 
   // Open two tabs.
   OpenURLParams open1(GURL(chrome::kChromeUIAboutURL), content::Referrer(),
                       NEW_BACKGROUND_TAB, ui::PAGE_TRANSITION_TYPED, false);
   int index_1 = GetIndex(browser()->OpenURL(open1));
 
   OpenURLParams open2(GURL(chrome::kChromeUICreditsURL), content::Referrer(),
                       NEW_BACKGROUND_TAB, ui::PAGE_TRANSITION_TYPED, false);
@@ skipping 42 matching lines @@
 
   // After removing the observer from the TabManager's list, it shouldn't
   // receive events anymore.
   tab_manager->RemoveObserver(&tabmanager_observer);
   EXPECT_TRUE(tab_manager->DiscardTabById(ContentsId(GetContents(index_1))));
   EXPECT_EQ(4, tabmanager_observer.nb_events());
 }
 
 IN_PROC_BROWSER_TEST_F(TabManagerObserverTest, OnAutoDiscardableStateChange) {
   TabManager* tab_manager = g_browser_process->GetTabManager();
-  ASSERT_TRUE(tab_manager);
   auto tsm = browser()->tab_strip_model();
   set_tab_strip_model(tsm);
 
   // Open two tabs.
   OpenURLParams open(GURL(chrome::kChromeUIAboutURL), content::Referrer(),
                      NEW_BACKGROUND_TAB, ui::PAGE_TRANSITION_TYPED, false);
   WebContents* contents = browser()->OpenURL(open);
 
   // Subscribe observer to TabManager's observer list.
   MockTabManagerObserver observer;
@@ skipping 19 matching lines @@
   // Change it back and we should have another event.
   tab_manager->SetTabAutoDiscardableState(contents, true);
   EXPECT_EQ(2, observer.nb_events());
   EXPECT_TRUE(observer.is_auto_discardable());
   EXPECT_EQ(ContentsId(contents), ContentsId(observer.content()));
 }
 
 }  // namespace memory
 
 #endif  // OS_WIN || OS_MAXOSX || OS_LINUX