Move more metrics classes to metrics namespace.

components/metrics/metrics_log.cc

Index: components/metrics/metrics_log.cc
diff --git a/components/metrics/metrics_log.cc b/components/metrics/metrics_log.cc
index 6076f88a82966bc3b1d21bb3c3a728af4e4954d0..314200d8f07231accc9e84d733c92070b15c20b4 100644
--- a/components/metrics/metrics_log.cc
+++ b/components/metrics/metrics_log.cc
@@ -43,12 +43,10 @@ extern "C" IMAGE_DOS_HEADER __ImageBase;
 #endif
 
 using base::SampleCountIterator;
-using metrics::HistogramEventProto;
-using metrics::ProfilerEventProto;
-using metrics::SystemProfileProto;
-using metrics::UserActionEventProto;
 typedef variations::ActiveGroupId ActiveGroupId;
 
+namespace metrics {
+
 namespace {
 
 // Any id less than 16 bytes is considered to be a testing id.
@@ -435,3 +433,5 @@ void MetricsLog::GetEncodedLog(std::string* encoded_log) {
   DCHECK(closed_);
   uma_proto_.SerializeToString(encoded_log);
 }
+
+}  // namespace metrics