Split a MetricsLogStore object out of MetricsLogManager.

components/metrics/BUILD.gn

Index: components/metrics/BUILD.gn
diff --git a/components/metrics/BUILD.gn b/components/metrics/BUILD.gn
index 129f1fe1da9e5fae8be1c56ed08ce7b06f9025a8..35b57624c6f68bde59044e6f9595910cf0147320 100644
--- a/components/metrics/BUILD.gn
+++ b/components/metrics/BUILD.gn
@@ -35,6 +35,7 @@ static_library("metrics") {
     "file_metrics_provider.h",
     "histogram_encoder.cc",
     "histogram_encoder.h",
+    "log_store.h",
     "machine_id_provider.h",
     "machine_id_provider_stub.cc",
     "machine_id_provider_win.cc",
@@ -42,6 +43,8 @@ static_library("metrics") {
     "metrics_log.h",
     "metrics_log_manager.cc",
     "metrics_log_manager.h",
+    "metrics_log_store.cc",
+    "metrics_log_store.h",
     "metrics_log_uploader.cc",
     "metrics_log_uploader.h",
     "metrics_pref_names.cc",
@@ -320,6 +323,7 @@ source_set("unit_tests") {
     "histogram_encoder_unittest.cc",
     "machine_id_provider_win_unittest.cc",
     "metrics_log_manager_unittest.cc",
+    "metrics_log_store_unittest.cc",
     "metrics_log_unittest.cc",
     "metrics_reporting_scheduler_unittest.cc",
     "metrics_service_unittest.cc",