[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 aac8afa60c469e67337e8ded3fe2a9e2d5abfcf8..e8fe20f5b077bc040149ef8c05b013fb2018753f 100644
--- a/content/browser/renderer_host/render_process_host_impl.h
+++ b/content/browser/renderer_host/render_process_host_impl.h
@@ -184,6 +184,7 @@ class CONTENT_EXPORT RenderProcessHostImpl
   void ForceReleaseWorkerRefCounts() override;
   bool IsWorkerRefCountDisabled() override;
   void PurgeAndSuspend() override;
+  const base::TimeTicks& GetLastPurgeAndSuspendTime() const override;
 
   mojom::RouteProvider* GetRemoteRouteProvider();
 
@@ -491,6 +492,8 @@ 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_;