Basic UkmService implementation

components/metrics/test_metrics_service_client.cc

Index: components/metrics/test_metrics_service_client.cc
diff --git a/components/metrics/test_metrics_service_client.cc b/components/metrics/test_metrics_service_client.cc
index 656fecc7f742c8c4576373e663940957650f0593..31e520ecdbb75084a0d72497ae70a7a4b17f36ba 100644
--- a/components/metrics/test_metrics_service_client.cc
+++ b/components/metrics/test_metrics_service_client.cc
@@ -4,12 +4,34 @@
 
 #include "components/metrics/test_metrics_service_client.h"
 
+#include <memory>
+
 #include "base/callback.h"
 #include "components/metrics/metrics_log_uploader.h"
 #include "components/metrics/proto/chrome_user_metrics_extension.pb.h"
 
 namespace metrics {
 
+namespace {
+
+class TestMetricsLogUploader : public MetricsLogUploader {
+ public:
+  TestMetricsLogUploader(const std::string& server_url,
+                         const std::string& mime_type,
+                         const base::Callback<void(int)>& on_upload_complete)
+      : MetricsLogUploader(server_url, mime_type, on_upload_complete) {}
+  ~TestMetricsLogUploader() override = default;
+
+  // MetricsLogUploader:
+  void UploadLog(const std::string& compressed_log_data,
+                 const std::string& log_hash) override {
+    // Never succeeds at uploading.
+    on_upload_complete_.Run(404);
+  }
+};
+
+}  // namespace
+
 // static
 const char TestMetricsServiceClient::kBrandForTesting[] = "brand_for_testing";
 
@@ -66,7 +88,8 @@ std::unique_ptr<MetricsLogUploader> TestMetricsServiceClient::CreateUploader(
     const std::string& server_url,
     const std::string& mime_type,
     const base::Callback<void(int)>& on_upload_complete) {
-  return std::unique_ptr<MetricsLogUploader>();
+  return std::unique_ptr<MetricsLogUploader>(
+      new TestMetricsLogUploader(server_url, mime_type, on_upload_complete));
 }
 
 base::TimeDelta TestMetricsServiceClient::GetStandardUploadInterval() {