Move the thread hop for UMA user actions from content:: to base::.

ios/chrome/browser/metrics/ios_chrome_metrics_service_client.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 IOS_CHROME_BROWSER_METRICS_IOS_CHROME_METRICS_SERVICE_CLIENT_H_
 #define IOS_CHROME_BROWSER_METRICS_IOS_CHROME_METRICS_SERVICE_CLIENT_H_
 
 #include <stdint.h>
 
 #include <memory>
@@ skipping 50 matching lines @@
   bool GetBrand(std::string* brand_code) override;
   metrics::SystemProfileProto::Channel GetChannel() override;
   std::string GetVersionString() override;
   void OnLogUploadComplete() override;
   void InitializeSystemProfileMetrics(
       const base::Closure& done_callback) override;
   void CollectFinalMetricsForLog(const base::Closure& done_callback) override;
   std::unique_ptr<metrics::MetricsLogUploader> CreateUploader(
       const base::Callback<void(int)>& on_upload_complete) override;
   base::TimeDelta GetStandardUploadInterval() override;
+  scoped_refptr<base::SingleThreadTaskRunner>
+      GetMainThreadTaskRunner() override;
   base::string16 GetRegistryBackupKey() override;
   void OnRendererProcessCrash() override;
 
+  // Returns the task runner for the main thread.

[Ilya Sherman, 2016/04/09 07:06:11]

?

[beaudoin, 2016/04/12 18:47:23]

Done.

+
   // web::GlobalWebStateObserver:
   void WebStateDidStartLoading(web::WebState* web_state) override;
   void WebStateDidStopLoading(web::WebState* web_state) override;
 
  private:
   explicit IOSChromeMetricsServiceClient(
       metrics::MetricsStateManager* state_manager);
 
   // Completes the two-phase initialization of IOSChromeMetricsServiceClient.
   void Initialize();
@@ skipping 71 matching lines @@
   // Whether this client has already uploaded profiler data during this session.
   // Profiler data is uploaded at most once per session.
   bool has_uploaded_profiler_data_;
 
   base::WeakPtrFactory<IOSChromeMetricsServiceClient> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(IOSChromeMetricsServiceClient);
 };
 
 #endif  // IOS_CHROME_BROWSER_METRICS_IOS_CHROME_METRICS_SERVICE_CLIENT_H_