[Sync] Implement MemoryDumpProvider.

components/sync/syncable/entry_kernel.cc

Index: components/sync/syncable/entry_kernel.cc
diff --git a/components/sync/syncable/entry_kernel.cc b/components/sync/syncable/entry_kernel.cc
index 2aaf8d1dcd9126f672aab637395ce27e64d3aea5..b707ffe2a1633b206953c6909f85894c7f87f9f1 100644
--- a/components/sync/syncable/entry_kernel.cc
+++ b/components/sync/syncable/entry_kernel.cc
@@ -8,7 +8,9 @@
 
 #include "base/json/string_escape.h"
 #include "base/strings/string_number_conversions.h"
+#include "base/trace_event/estimate_memory_usage.h"
 #include "components/sync/base/cryptographer.h"
+#include "components/sync/protocol/proto_memory_estimations.h"
 #include "components/sync/protocol/proto_value_conversions.h"
 #include "components/sync/syncable/syncable_columns.h"
 #include "components/sync/syncable/syncable_enum_conversions.h"
@@ -16,7 +18,7 @@
 namespace syncer {
 namespace syncable {
 
-EntryKernel::EntryKernel() : dirty_(false) {
+EntryKernel::EntryKernel() : dirty_(false), memory_usage_(kMemoryUsageUnknown) {
   // Everything else should already be default-initialized.
   for (int i = 0; i < INT64_FIELDS_COUNT; ++i) {
     int64_fields[i] = 0;
@@ -211,6 +213,19 @@ base::DictionaryValue* EntryKernel::ToValue(
   return kernel_info;
 }
 
+size_t EntryKernel::EstimateMemoryUsage() const {
+  if (memory_usage_ == kMemoryUsageUnknown) {
+    using base::trace_event::EstimateMemoryUsage;
+    memory_usage_ =
+        EstimateMemoryUsage(string_fields) +
+        EstimateMemoryUsage(specifics_fields) +
+        EstimateMemoryUsage(id_fields) +
+        EstimateMemoryUsage(unique_position_fields) +
+        EstimateMemoryUsage(attachment_metadata_fields);
+  }
+  return memory_usage_;
+}
+
 std::unique_ptr<base::ListValue> EntryKernelMutationMapToValue(
     const EntryKernelMutationMap& mutations) {
   std::unique_ptr<base::ListValue> list(new base::ListValue());