Create and integrate a metrics service client into Blimp engine.

blimp/engine/common/blimp_browser_context.h

Index: blimp/engine/common/blimp_browser_context.h
diff --git a/blimp/engine/common/blimp_browser_context.h b/blimp/engine/common/blimp_browser_context.h
index e02f8316a035d7c664a56e02dd1ce6a5dabf55e4..b3b9f63aa3a9228470499f7050deb2df0e5f6169 100644
--- a/blimp/engine/common/blimp_browser_context.h
+++ b/blimp/engine/common/blimp_browser_context.h
@@ -9,6 +9,7 @@
 
 #include "base/files/file_path.h"
 #include "base/macros.h"
+#include "blimp/engine/app/blimp_metrics_service_client.h"
 #include "blimp/engine/app/blimp_system_url_request_context_getter.h"
 #include "blimp/engine/app/blimp_url_request_context_getter.h"
 #include "content/public/browser/browser_context.h"
@@ -67,6 +68,10 @@ class BlimpBrowserContext : public content::BrowserContext {
   // allowed on the current thread.
   void InitWhileIOAllowed();
 
+  // Used in metrics initialization to get a PrefService to store logs
+  // temporarily.
+  std::unique_ptr<PrefService> GetPrefService();
+
   std::unique_ptr<BlimpResourceContext> resource_context_;
   scoped_refptr<BlimpSystemURLRequestContextGetter> system_context_getter_;
   bool ignore_certificate_errors_;