Use TimeTicks as much as possible in startup_metric_utils.

mandoline/ui/desktop_ui/browser_manager.h

 // Copyright 2015 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 MANDOLINE_UI_DESKTOP_UI_BROWSER_MANAGER_H_
 #define MANDOLINE_UI_DESKTOP_UI_BROWSER_MANAGER_H_
 
 #include <set>
 
 #include "components/mus/public/interfaces/window_tree_host.mojom.h"
@@ skipping 19 matching lines @@
  public:
   BrowserManager();
   ~BrowserManager() override;
 
   // BrowserManager owns the returned BrowserWindow.
   BrowserWindow* CreateBrowser(const GURL& default_url);
 
   void BrowserWindowClosed(BrowserWindow* browser);
 
   // Get the time recorded just before the application message loop was started.
-  const base::Time& startup_time() const { return startup_time_; }
+  const base::TimeTicks& startup_ticks() const { return startup_ticks_; }
 
  private:
   // Overridden from LaunchHandler:
   void LaunchURL(const mojo::String& url) override;
 
   // Overridden from mojo::ApplicationDelegate:
   void Initialize(mojo::ApplicationImpl* app) override;
   bool ConfigureIncomingConnection(
       mojo::ApplicationConnection* connection) override;
 
   // Overridden from mojo::InterfaceFactory<LaunchHandler>:
   void Create(mojo::ApplicationConnection* connection,
               mojo::InterfaceRequest<LaunchHandler> request) override;
 
   mojo::ApplicationImpl* app_;
   mus::mojom::WindowTreeHostFactoryPtr host_factory_;
   mojo::WeakBindingSet<LaunchHandler> launch_handler_bindings_;
   std::set<BrowserWindow*> browsers_;
-  base::Time startup_time_;
+  const base::TimeTicks startup_ticks_;
 
   DISALLOW_COPY_AND_ASSIGN(BrowserManager);
 };
 
 }  // namespace mandoline
 
 #endif  // MANDOLINE_UI_DESKTOP_UI_BROWSER_MANAGER_H_