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..2910bb1afafa1396af0d0d408d8a433afbdefc4b 100644
--- a/net/disk_cache/memory/mem_entry_impl.cc
+++ b/net/disk_cache/memory/mem_entry_impl.cc
@@ -253,6 +253,14 @@ int MemEntryImpl::ReadyForSparseIO(const CompletionCallback& callback) {
   return net::OK;
 }
 
+size_t MemEntryImpl::EstimateMemoryUsage() const {
+  // Subtlety: the entries in children_ are not double counted, as the entry
+  // pointers won't be followed by EstimateMemoryUsage.
+  return base::trace_event::EstimateMemoryUsage(data_) +
+         base::trace_event::EstimateMemoryUsage(key_) +
+         base::trace_event::EstimateMemoryUsage(children_);
+}
+
 // ------------------------------------------------------------------------
 
 MemEntryImpl::MemEntryImpl(MemBackendImpl* backend,