Keep track of byte usage of the memory cache backend

net/disk_cache/memory/mem_backend_impl.cc

 // Copyright (c) 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.
 
 #include "net/disk_cache/memory/mem_backend_impl.h"
 
 #include <algorithm>
 #include <functional>
 #include <utility>
 
 #include "base/logging.h"
 #include "base/memory/ptr_util.h"
 #include "base/sys_info.h"
+#include "base/trace_event/memory_usage_estimator.h"
 #include "net/base/net_errors.h"
 #include "net/disk_cache/cache_util.h"
 #include "net/disk_cache/memory/mem_entry_impl.h"
 
 using base::Time;
 
 namespace disk_cache {
 
 namespace {
 
@@ skipping 253 matching lines @@
       new MemIterator(weak_factory_.GetWeakPtr()));
 }
 
 void MemBackendImpl::OnExternalCacheHit(const std::string& key) {
   EntryMap::iterator it = entries_.find(key);
   if (it != entries_.end())
     it->second->UpdateStateOnUse(MemEntryImpl::ENTRY_WAS_NOT_MODIFIED);
 }
 
 size_t MemBackendImpl::EstimateMemoryUsage() const {
-  // TODO(xunjieli): Implement this. crbug.com/669108.
-  return 0;
+  // Entries in lru_list_ will be counted by EMU but not in entries_ since
+  // they're pointers.
+  return base::trace_event::EstimateMemoryUsage(lru_list_) +
+         base::trace_event::EstimateMemoryUsage(entries_);
 }
 
 void MemBackendImpl::EvictIfNeeded() {
   if (current_size_ <= max_size_)
     return;
 
   int target_size = std::max(0, max_size_ - kDefaultEvictionSize);
 
   base::LinkNode<MemEntryImpl>* entry = lru_list_.head();
   while (current_size_ > target_size && entry != lru_list_.end()) {
     MemEntryImpl* to_doom = entry->value();
     entry = entry->next();
     if (!to_doom->InUse())
       to_doom->Doom();
   }
 }
 
 }  // namespace disk_cache