base: Use range-based for loops in DiscardableMemoryManager.

base/memory/discardable_memory_manager.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 "base/memory/discardable_memory_manager.h"
 
 #include "base/bind.h"
+#include "base/containers/adapters.h"
 #include "base/containers/hash_tables.h"
 #include "base/containers/mru_cache.h"
 #include "base/debug/crash_logging.h"
 #include "base/debug/trace_event.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/synchronization/lock.h"
 
 namespace base {
 namespace internal {
 
@@ skipping 152 matching lines @@
   return bytes_allocated_ <= soft_memory_limit_;
 }
 
 void DiscardableMemoryManager::
     PurgeIfNotUsedSinceTimestampUntilUsageIsWithinLimitWithLockAcquired(
         TimeTicks timestamp,
         size_t limit) {
   lock_.AssertAcquired();
 
   size_t bytes_allocated_before_purging = bytes_allocated_;
-  for (AllocationMap::reverse_iterator it = allocations_.rbegin();
-       it != allocations_.rend();
-       ++it) {
-    Allocation* allocation = it->first;
-    AllocationInfo* info = &it->second;
+  for (auto& entry : base::Reversed(allocations_)) {
+    Allocation* allocation = entry.first;
+    AllocationInfo* info = &entry.second;
 
     if (bytes_allocated_ <= limit)
       break;
 
     bool purgable = info->purgable && info->last_usage <= timestamp;
     if (!purgable)
       continue;
 
     size_t bytes_purgable = info->bytes;
     DCHECK_LE(bytes_purgable, bytes_allocated_);
@@ skipping 15 matching lines @@
   base::debug::SetCrashKeyValue(kDiscardableMemoryUsageKey,
                                 Uint64ToString(new_bytes_allocated));
 }
 
 TimeTicks DiscardableMemoryManager::Now() const {
   return TimeTicks::Now();
 }
 
 }  // namespace internal
 }  // namespace base