Reland "Make MetricsLog not need a PrefService."

Sorry, I reverted wrong cl.

BUG: 751948
[email protected],[email protected],[email protected]

This is a reland of 433d691752d8d327b99e5432c8f280e3f2ff8b83
Original change's description:
> Make MetricsLog not need a PrefService.
> 
> Move system profile persistence to MetricsService.
> 
> Bug: 
> Change-Id: I5c31dc53de267dd9699a83af926f8a575bab18a0
> Reviewed-on: https://chromium-review.googlesource.com/592689
> Commit-Queue: Steven Holte <[email protected]>
> Reviewed-by: Olivier Robin <[email protected]>
> Reviewed-by: Brian White <[email protected]>
> Cr-Commit-Position: refs/heads/master@{#491573}

Change-Id: Iea3ebc29e92f3e12fc56f7b7ba767c531f216041
Reviewed-on: https://chromium-review.googlesource.com/598759
Commit-Queue: Tsuyoshi Horo <[email protected]>
Reviewed-by: Tsuyoshi Horo <[email protected]>
Cr-Commit-Position: refs/heads/master@{#491684}
diff --git a/components/metrics/metrics_log_store_unittest.cc b/components/metrics/metrics_log_store_unittest.cc
index 5c35274..50b78c7 100644
--- a/components/metrics/metrics_log_store_unittest.cc
+++ b/components/metrics/metrics_log_store_unittest.cc
@@ -21,7 +21,7 @@
   ~MetricsLogStoreTest() override {}
 
   MetricsLog* CreateLog(MetricsLog::LogType log_type) {
-    return new MetricsLog("id", 0, log_type, &client_, &pref_service_);
+    return new MetricsLog("id", 0, log_type, &client_);
   }
 
   // Returns the stored number of logs of the given type.