Keep track of byte usage of the memory cache backend

base/trace_event/memory_usage_estimator.h

Index: base/trace_event/memory_usage_estimator.h
diff --git a/base/trace_event/memory_usage_estimator.h b/base/trace_event/memory_usage_estimator.h
index 1f4132bdcb2dcf29cd0396fe7c2ac691b0e6769b..e8ac89fc28a423e85f72ce81f6f3bf7c4f11d493 100644
--- a/base/trace_event/memory_usage_estimator.h
+++ b/base/trace_event/memory_usage_estimator.h
@@ -22,6 +22,7 @@
 #include <vector>
 
 #include "base/base_export.h"
+#include "base/containers/linked_list.h"
 #include "base/strings/string16.h"
 #include "base/template_util.h"
 
@@ -111,6 +112,9 @@ size_t EstimateMemoryUsage(const std::vector<T, A>& vector);
 template <class T, class A>
 size_t EstimateMemoryUsage(const std::list<T, A>& list);
 
+template <class T>
+size_t EstimateMemoryUsage(const base::LinkedList<T>& list);
+
 template <class T, class C, class A>
 size_t EstimateMemoryUsage(const std::set<T, C, A>& set);
 
@@ -352,6 +356,18 @@ size_t EstimateMemoryUsage(const std::list<T, A>& list) {
          EstimateIterableMemoryUsage(list);
 }
 
+template <class T>
+size_t EstimateMemoryUsage(const base::LinkedList<T>& list) {
+  size_t memory_usage = sizeof(LinkedList<T>);

[DmitrySkiba, 2017/02/27 19:17:42]

We don't need to account for LinkedList static size here - it's done on a higher
level. I.e. if LinkedList is dynamically allocated, then
EMU(unique_ptr<LinkedList>) will take care of accounting for sizeof(LinkedList).
See how EMU(list) is implemented, for example.

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

Done.

+  for (base::LinkNode<T>* node = list.head(); node != list.end();
+       node = node->next()) {
+    // Since we increment by calling node = node->next() we know that node
+    // isn't nullptr.
+    memory_usage += EstimateMemoryUsage(*node->value());

[Primiano Tucci (use gerrit), 2017/02/27 18:14:53]

shouldn't this also be + sizeof(base::LinkNode<T>) ? or maybe just *node ?

[DmitrySkiba, 2017/02/27 19:17:42]

Yup. Since nodes are (likely) heap allocated, we need to also add static size of
node here. However, since LinkNode<T> is included in T (as implied by its
value() method), we need to use sizeof(T).

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

Done.

+  }
+  return memory_usage;
+}
+
 // Tree containers
 
 template <class V>