Use container::back() and container::pop_back() for content.

content/browser/indexed_db/indexed_db_active_blob_registry_unittest.cc

 // Copyright 2014 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 <stdint.h>
 
 #include <set>
 
 #include "base/macros.h"
 #include "base/test/test_simple_task_runner.h"
@@ skipping 23 matching lines @@
     } else {
       if (!origins_.count(origin)) {
         duplicate_calls_ = true;
       } else {
         origins_.erase(origin);
       }
     }
   }
 
   bool CheckNoOriginsInUse() const {
-    return !duplicate_calls_ && !origins_.size();
+    return !duplicate_calls_ && origins_.empty();
   }
 
   bool CheckSingleOriginInUse(const url::Origin& origin) const {
     return !duplicate_calls_ && origins_.size() == 1 && origins_.count(origin);
   }
 
  private:
   ~RegistryTestMockFactory() override {}
 
   std::set<url::Origin> origins_;
@@ skipping 217 matching lines @@
   RunUntilIdle();
 
   // Nothing changes.
   EXPECT_TRUE(factory()->CheckSingleOriginInUse(backing_store()->origin()));
   EXPECT_TRUE(backing_store()->CheckUnusedBlobsEmpty());
 }
 
 }  // namespace
 
 }  // namespace content