Changes PlzNavitate histograms to try and simplify their multi-modal characteristic.

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 92d1e4d1b78802735102f58033d32dd093bc8679..383e199495be91637d4305898f6c9277d5b83611 100644
--- a/content/browser/renderer_host/render_process_host_impl.h
+++ b/content/browser/renderer_host/render_process_host_impl.h
@@ -139,6 +139,7 @@ class CONTENT_EXPORT RenderProcessHostImpl
       OVERRIDE;
   virtual void NotifyTimezoneChange() OVERRIDE;
   virtual ServiceRegistry* GetServiceRegistry() OVERRIDE;
+  virtual const base::TimeTicks& GetInitTime() const OVERRIDE;
 
   // IPC::Sender via RenderProcessHost.
   virtual bool Send(IPC::Message* msg) OVERRIDE;
@@ -371,6 +372,10 @@ class CONTENT_EXPORT RenderProcessHostImpl
   // also reset that in the case of process termination.
   bool is_initialized_;
 
+  // The time at which the first call to Init happened and the child renderer
+  // process was created.
+  base::TimeTicks init_time_;
+
   // Used to launch and terminate the process without blocking the UI thread.
   scoped_ptr<ChildProcessLauncher> child_process_launcher_;