Added UkmPageLoadMetricsObserver which sends top-level metrics to UKM

components/ukm/test_ukm_service.h

 // Copyright 2017 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef COMPONENTS_UKM_TEST_UKM_SERVICE_H_
 #define COMPONENTS_UKM_TEST_UKM_SERVICE_H_
 
 #include <stddef.h>
 #include <memory>
 
@@ skipping 19 matching lines @@
   DISALLOW_COPY_AND_ASSIGN(TestUkmService);
 };
 
 // Convenience harness used for testing; creates a TestUkmService and
 // supplies it with a prefs service with a longer lifespan.
 class UkmServiceTestingHarness {
  public:
   UkmServiceTestingHarness();
   virtual ~UkmServiceTestingHarness();
 
-  const TestUkmService& test_ukm_service() const {
-    return *test_ukm_service_.get();
-  }
+  TestUkmService* test_ukm_service() { return test_ukm_service_.get(); }
 
  private:
   TestingPrefServiceSimple test_prefs_;
   std::unique_ptr<TestUkmService> test_ukm_service_;
 
   DISALLOW_COPY_AND_ASSIGN(UkmServiceTestingHarness);
 };
 
 }  // namespace ukm
 
 #endif  // COMPONENTS_UKM_TEST_UKM_SERVICE_H_