[Sync] Implement MemoryDumpProvider.

components/sync/base/unique_position.cc

Index: components/sync/base/unique_position.cc
diff --git a/components/sync/base/unique_position.cc b/components/sync/base/unique_position.cc
index 685a290e3e0df4be30ea5a48def3e12af340592a..3e802e827ab5c387824b96835a781843217776ee 100644
--- a/components/sync/base/unique_position.cc
+++ b/components/sync/base/unique_position.cc
@@ -11,6 +11,7 @@
 #include "base/rand_util.h"
 #include "base/stl_util.h"
 #include "base/strings/string_number_conversions.h"
+#include "base/trace_event/memory_usage_estimator.h"
 #include "components/sync/protocol/unique_position.pb.h"
 #include "third_party/zlib/zlib.h"
 
@@ -614,4 +615,9 @@ bool UniquePosition::IsValidCompressed(const std::string& str) {
   return true;
 }
 
+size_t UniquePosition::EstimateMemoryUsage() const {
+  using base::trace_event::EstimateMemoryUsage;
+  return EstimateMemoryUsage(compressed_);
+}
+
 }  // namespace syncer