[Sync] Implement MemoryDumpProvider.

components/sync/protocol/proto_memory_estimations.cc

+// Copyright (c) 2016 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.
+
+// Keep this file in sync with the .proto files in this directory.
+
+#include "components/sync/protocol/proto_memory_estimations.h"
+
+#include "base/trace_event/memory_usage_estimator.h"
+#include "components/sync/protocol/proto_visitors.h"
+
+namespace {
+
+// This class is a VisitProtoFields()-compatible visitor that estimates
+// proto's memory usage:
+//
+//  MemoryUsageVisitor visitor;
+//  VisitProtoFields(visitor, proto);
+//  size_t memory_usage = visitor.memory_usage();
+//
+class MemoryUsageVisitor {
+ public:
+  MemoryUsageVisitor() : memory_usage_(0) {}
+
+  size_t memory_usage() const { return memory_usage_; }
+
+  template <class P>
+  void VisitBytes(const P& parent_proto,
+                  const char* field_name,
+                  const std::string& field) {
+    // Delegate to Visit(..., const std::string&) below.
+    Visit(parent_proto, field_name, field);
+  }
+
+  template <class P, class E>
+  void VisitEnum(const P&, const char* field_name, E field) {}
+
+  // Types derived from MessageLite (i.e. protos)
+  template <class P, class F>
+  typename std::enable_if<
+      std::is_base_of<google::protobuf::MessageLite, F>::value>::type
+  Visit(const P&, const char* field_name, const F& field) {
+    using base::trace_event::EstimateMemoryUsage;
+    // All object fields are dynamically allocated.
+    memory_usage_ += sizeof(F) + EstimateMemoryUsage(field);
+  }
+
+  // Integral types
+  template <class P, class F>
+  typename std::enable_if<std::is_integral<F>::value>::type
+  Visit(const P&, const char* field_name, const F& field) {
+    // Integral fields (integers, floats & bool) don't allocate.
+  }
+
+  // std::string
+  template <class P>
+  void Visit(const P&, const char* field_name, const std::string& field) {
+    using base::trace_event::EstimateMemoryUsage;
+    // All strings are of type ArenaStringPtr, which essentially
+    // is std::string*.
+    memory_usage_ += sizeof(std::string) + EstimateMemoryUsage(field);
+  }
+
+  // RepeatedPtrField
+  template <class P, class F>
+  void Visit(const P&,
+             const char* field_name,
+             const google::protobuf::RepeatedPtrField<F>& fields) {
+    using base::trace_event::EstimateMemoryUsage;
+    // Can't use RepeatedPtrField::SpaceUsedExcludingSelf() because it will
+    // end up calling undefined TypeHandler::SpaceUsed() method.
+    memory_usage_ += fields.Capacity() ? sizeof(void*) : 0;  // header
+    memory_usage_ += fields.Capacity() * sizeof(void*);
+    for (const auto& field : fields) {
+      memory_usage_ += sizeof(F) + EstimateMemoryUsage(field);
+    }
+  }
+
+  // RepeatedField<integral type>
+  template <class P, class F>
+  typename std::enable_if<std::is_integral<F>::value>::type Visit(
+      const P&,
+      const char* field_name,
+      const google::protobuf::RepeatedField<F>& fields) {
+    memory_usage_ += fields.SpaceUsedExcludingSelf();
+    // Integral fields (integers, floats & bool) don't allocate, so no
+    // point in iterating over |fields|.
+  }
+
+  // RepeatedField<std::string>
+  template <class P>
+  void Visit(const P&,
+             const char* field_name,
+             const google::protobuf::RepeatedField<std::string>& fields) {
+    using base::trace_event::EstimateMemoryUsage;
+    memory_usage_ += fields.SpaceUsedExcludingSelf();
+    for (const auto& field : fields) {
+      memory_usage_ += EstimateMemoryUsage(field);
+    }
+  }
+
+ private:
+  size_t memory_usage_;
+};
+
+}  // namespace
+
+namespace sync_pb {
+
+template <class P>
+size_t EstimateMemoryUsage(const P& proto) {
+  MemoryUsageVisitor visitor;
+  syncer::VisitProtoFields(visitor, proto);
+  return visitor.memory_usage();
+}
+
+// Explicit instantiations
+
+#define INSTANTIATE(Proto) \
+  template size_t EstimateMemoryUsage<Proto>(const Proto&);
+
+INSTANTIATE(EntitySpecifics)
+INSTANTIATE(AttachmentMetadata)
+INSTANTIATE(DataTypeContext)
+
+}  // namespace sync_pb