Remove PRODUCT_STRING_PATH from chrome_constants.h on Windows.

components/browser_watcher/watcher_metrics_provider_win.h

 // Copyright (c) 2014 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 COMPONENTS_BROWSER_WATCHER_WATCHER_METRICS_PROVIDER_WIN_H_
 #define COMPONENTS_BROWSER_WATCHER_WATCHER_METRICS_PROVIDER_WIN_H_
 
 #include "base/macros.h"
 #include "base/strings/string16.h"
 #include "base/task_runner.h"
 #include "components/metrics/metrics_provider.h"
 
 namespace browser_watcher {
 
 // Provides stability data captured by the Chrome Watcher, namely the browser
 // process exit codes.
 class WatcherMetricsProviderWin : public metrics::MetricsProvider {
  public:
   static const char kBrowserExitCodeHistogramName[];
 
   // Initializes the reporter. |cleanup_io_task_runner| is used to clear
   // leftover data in registry if metrics reporting is disabled.
-  WatcherMetricsProviderWin(const base::char16* registry_path,
+  WatcherMetricsProviderWin(const base::string16& registry_path,
                             base::TaskRunner* cleanup_io_task_runner);
   ~WatcherMetricsProviderWin() override;
 
   // metrics::MetricsProvider implementation.
   void OnRecordingEnabled() override;
   void OnRecordingDisabled() override;
   void ProvideStabilityMetrics(
       metrics::SystemProfileProto* system_profile_proto) override;
 
  private:
   bool recording_enabled_;
   bool cleanup_scheduled_;
-  base::string16 registry_path_;
+  const base::string16 registry_path_;
   scoped_refptr<base::TaskRunner> cleanup_io_task_runner_;
 
   DISALLOW_COPY_AND_ASSIGN(WatcherMetricsProviderWin);
 };
 
 }  // namespace browser_watcher
 
 #endif  // COMPONENTS_BROWSER_WATCHER_WATCHER_METRICS_PROVIDER_WIN_H_