[Tentaive patch for discussion] Add Purge+Suspend metrics as UMA.

content/browser/renderer_host/render_process_host_impl.h

Index: content/browser/renderer_host/render_process_host_impl.h
diff --git a/content/browser/renderer_host/render_process_host_impl.h b/content/browser/renderer_host/render_process_host_impl.h
index 6e6a0f27ced9be3c8d4d09c5f1aa72e5800bc035..530070942db7e648e9b104fccc120c51a3d7c1a5 100644
--- a/content/browser/renderer_host/render_process_host_impl.h
+++ b/content/browser/renderer_host/render_process_host_impl.h
@@ -179,6 +179,7 @@ class CONTENT_EXPORT RenderProcessHostImpl
   void ForceReleaseWorkerRefCounts() override;
   bool IsWorkerRefCountDisabled() override;
   void PurgeAndSuspend() override;
+  const base::TimeTicks& GetLastPurgeAndSuspendTime() const override;
 
   mojom::RouteProvider* GetRemoteRouteProvider();
 
@@ -477,6 +478,8 @@ class CONTENT_EXPORT RenderProcessHostImpl
   // Stores the time at which the first call to Init happened.
   base::TimeTicks init_time_;
 
+  base::TimeTicks last_purge_and_suspend_time_;
+
   // Used to launch and terminate the process without blocking the UI thread.
   std::unique_ptr<ChildProcessLauncher> child_process_launcher_;