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

content/public/browser/render_process_host.h

Index: content/public/browser/render_process_host.h
diff --git a/content/public/browser/render_process_host.h b/content/public/browser/render_process_host.h
index 8f7e45e4fe9b986f01a64fb898a7d541aa76b260..7a8b07e87c5be86cc1de22d714c5b4c35ae1591b 100644
--- a/content/public/browser/render_process_host.h
+++ b/content/public/browser/render_process_host.h
@@ -317,6 +317,8 @@ class CONTENT_EXPORT RenderProcessHost : public IPC::Sender,
   // Purges and suspends the renderer process.
   virtual void PurgeAndSuspend() = 0;
 
+  virtual const base::TimeTicks& GetLastPurgeAndSuspendTime() const = 0;
+
   // Returns the current number of active views in this process.  Excludes
   // any RenderViewHosts that are swapped out.
   size_t GetActiveViewCount();