Basic UkmService implementation

components/metrics/metrics_service_client.h

Index: components/metrics/metrics_service_client.h
diff --git a/components/metrics/metrics_service_client.h b/components/metrics/metrics_service_client.h
index c1c28457a679fb760348bd56006dca9c48f3e6ce..858d1d87db491f533ddcc9611231115b1d41f6ba 100644
--- a/components/metrics/metrics_service_client.h
+++ b/components/metrics/metrics_service_client.h
@@ -20,6 +20,10 @@ namespace base {
 class FilePath;
 }
 
+namespace ukm {
+class UkmService;
+}
+
 namespace metrics {
 
 class MetricsLogUploader;
@@ -37,6 +41,9 @@ class MetricsServiceClient {
   // implementation will own the MetricsService instance being returned).
   virtual MetricsService* GetMetricsService() = 0;
 
+  // Returns the UkmService instance that this client is associated with.
+  virtual ukm::UkmService* GetUkmService();
+
   // Registers the client id with other services (e.g. crash reporting), called
   // when metrics recording gets enabled.
   virtual void SetMetricsClientId(const std::string& client_id) = 0;