Flush UKM metrics when backgrounded on Android and iOS.

ios/chrome/browser/application_context.h

Index: ios/chrome/browser/application_context.h
diff --git a/ios/chrome/browser/application_context.h b/ios/chrome/browser/application_context.h
index cf49fd29e30cd8d4fb7b6eac99a57a7e390ed042..0643826f8e87f12e6d14a8a3c69042d5cee93c51 100644
--- a/ios/chrome/browser/application_context.h
+++ b/ios/chrome/browser/application_context.h
@@ -49,6 +49,10 @@ namespace rappor {
 class RapporServiceImpl;
 }
 
+namespace ukm {
+class UkmService;
+}
+
 namespace variations {
 class VariationsService;
 }
@@ -99,6 +103,9 @@ class ApplicationContext {
   // Gets the MetricsService used by this application.
   virtual metrics::MetricsService* GetMetricsService() = 0;
 
+  // Gets the UkmService used by this application.
+  virtual ukm::UkmService* GetUkmService() = 0;
+
   // Gets the VariationsService used by this application.
   virtual variations::VariationsService* GetVariationsService() = 0;