Added accessor for the ukm service to the browser process singleton

chrome/browser/browser_process.h

Index: chrome/browser/browser_process.h
diff --git a/chrome/browser/browser_process.h b/chrome/browser/browser_process.h
index 3801f737f17630a10c32c6071cbfc1eb1b4dc0be..b11c732a9e05969dec211777f738bc9380c9ddb1 100644
--- a/chrome/browser/browser_process.h
+++ b/chrome/browser/browser_process.h
@@ -118,6 +118,10 @@ namespace safe_browsing {
 class ClientSideDetectionService;
 }
 
+namespace ukm {
+class UkmService;
+}
+
 // NOT THREAD SAFE, call only from the main thread.
 // These functions shouldn't return NULL unless otherwise noted.
 class BrowserProcess {
@@ -142,6 +146,7 @@ class BrowserProcess {
   // Services: any of these getters may return NULL
   virtual metrics::MetricsService* metrics_service() = 0;
   virtual rappor::RapporServiceImpl* rappor_service() = 0;
+  virtual ukm::UkmService* ukm_service() = 0;

[sky, 2017/01/24 22:38:01]

Can you outline why we need both GetMetricsServicesManager and this accessor,
which appears to be nothing more than a call to
GetMetricsServicesManager()->GetUkmService()?

[oystein (OOO til 10th of July), 2017/01/24 22:44:16]

I followed the example of rappor_service() and variations_service(), the main
purpose is to be able to overload it in testing_browser_process.h to return a
unit-test provided subclass of the service.

   virtual ProfileManager* profile_manager() = 0;
   virtual PrefService* local_state() = 0;
   virtual net::URLRequestContextGetter* system_request_context() = 0;