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

content/public/browser/render_process_host.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CONTENT_PUBLIC_BROWSER_RENDER_PROCESS_HOST_H_
 #define CONTENT_PUBLIC_BROWSER_RENDER_PROCESS_HOST_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 299 matching lines @@
   // After this is called, the Increment/DecrementWorkerRefCount functions must
   // not be called.
   virtual void ForceReleaseWorkerRefCounts() = 0;
 
   // Returns true if ForceReleaseWorkerRefCounts was called.
   virtual bool IsWorkerRefCountDisabled() = 0;
 
   // 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();
 
   // Static management functions -----------------------------------------------
 
   // Flag to run the renderer in process.  This is primarily
   // for debugging purposes.  When running "in process", the
   // browser maintains a single RenderProcessHost which communicates
   // to a RenderProcess which is instantiated in the same process
@@ skipping 42 matching lines @@
   static void SetMaxRendererProcessCount(size_t count);
 
   // Returns the current maximum number of renderer process hosts kept by the
   // content module.
   static size_t GetMaxRendererProcessCount();
 };
 
 }  // namespace content.
 
 #endif  // CONTENT_PUBLIC_BROWSER_RENDER_PROCESS_HOST_H_