Fix ios_chrome_unittests to crash on DCHECK failure.

ios/chrome/browser/ui/collection_view/collection_view_model_unittest.mm

 // Copyright 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.
 
 #import "ios/chrome/browser/ui/collection_view/collection_view_model.h"
 
 #include "base/mac/foundation_util.h"
 #include "base/mac/scoped_nsobject.h"
 #import "ios/chrome/browser/ui/collection_view/cells/collection_view_item.h"
 #include "testing/gtest/include/gtest/gtest.h"
@@ skipping 284 matching lines @@
   EXPECT_NSEQ(cheddar, cheeseItems[0]);
   EXPECT_NSEQ(pepperJack, cheeseItems[1]);
   EXPECT_NSEQ(gouda, cheeseItems[2]);
 }
 
 TEST(CollectionViewModelTest, InvalidIndexPath) {
   base::scoped_nsobject<CollectionViewModel> model(
       [[CollectionViewModel alloc] init]);
   [model addSectionWithIdentifier:SectionIdentifierCheese];
 
+  logging::SetLogAssertHandler(&LogSink);

[noyau (Ping after 24h), 2016/12/22 13:17:22]

Suggestions: This would probably be better is handled via a scoped object
resetting the log handler to its previous value when deallocated. Could be done
in a separate CL.

[sdefresne, 2016/12/22 13:28:12]

I agree (there is a similar scoped object in net/test/ but it install a
different assert handler). I'll do it in a followup CL.

   bool out_of_bounds_exception_thrown = false;
   @try {
-    logging::SetLogAssertHandler(&LogSink);
     [model indexInItemTypeForIndexPath:[NSIndexPath indexPathForItem:0
                                                            inSection:0]];
   } @catch (NSException* exception) {
     if ([[exception name] isEqualToString:NSRangeException]) {
       out_of_bounds_exception_thrown = true;
     }
   }
   EXPECT_TRUE(out_of_bounds_exception_thrown);
+  logging::SetLogAssertHandler(nullptr);
 }
 
 TEST(CollectionViewModelTest, RemoveItems) {
   base::scoped_nsobject<CollectionViewModel> model(
       [[CollectionViewModel alloc] init]);
 
   [model addSectionWithIdentifier:SectionIdentifierCheese];
   [model addItemWithType:ItemTypeCheesePepperJack
       toSectionWithIdentifier:SectionIdentifierCheese];
   [model addItemWithType:ItemTypeCheeseGouda
@@ skipping 256 matching lines @@
 
   EXPECT_FALSE([model footerForSectionWithIdentifier:SectionIdentifierCheese]);
   EXPECT_FALSE([model footerForSection:cheeseSection]);
 
   EXPECT_EQ(weasleyFooter.get(),
             [model footerForSectionWithIdentifier:SectionIdentifierWeasley]);
   EXPECT_EQ(weasleyFooter.get(), [model footerForSection:weasleySection]);
 }
 
 }  // namespace