Keep track of byte usage of the memory cache backend

net/disk_cache/memory/mem_entry_impl.cc

Index: net/disk_cache/memory/mem_entry_impl.cc
diff --git a/net/disk_cache/memory/mem_entry_impl.cc b/net/disk_cache/memory/mem_entry_impl.cc
index cfe23e75cf70066caf36a89ec77b05ded1f5af03..9153fea32ccddcc9dec1e94bfd5c59a0564a1e2e 100644
--- a/net/disk_cache/memory/mem_entry_impl.cc
+++ b/net/disk_cache/memory/mem_entry_impl.cc
@@ -253,6 +253,12 @@ int MemEntryImpl::ReadyForSparseIO(const CompletionCallback& callback) {
   return net::OK;
 }
 
+size_t MemEntryImpl::EstimateMemoryUsage() const {
+  return base::trace_event::EstimateMemoryUsage(data_) +
+         base::trace_event::EstimateMemoryUsage(key_) +
+         base::trace_event::EstimateMemoryUsage(children_);

[xunjieli, 2017/02/27 18:51:31]

I suppose the |children_| entries are accounted for in the backend's
|iru_list_|?

[jkarlin, 2017/02/28 13:10:50]

Ah, you're right. Switched to using GetStorageSize().

[xunjieli, 2017/02/28 14:51:23]

Ah, sorry for the confusion, the previous patchset is correct. Could you change
it back?
|children_| is a std::unique_ptr<std::unordered_map<int, MemEntryImpl*>>.
base::trace_event::EstimateMemoryUsage(children_) will count the size of the
MemEntryImpl pointer as stored in the map but not the underlying type. 

If the underlying MemEntryImpl are accounted for in the backend, then we are
good here. EMU(children_) gives exactly what we want (the allocation is just for
the map and there is no double counting of the underlying MemEntryImpl).

[jkarlin, 2017/02/28 15:50:54]

Done.

+}
+
 // ------------------------------------------------------------------------
 
 MemEntryImpl::MemEntryImpl(MemBackendImpl* backend,