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

chrome/browser/chrome_browser_main.cc

Index: chrome/browser/chrome_browser_main.cc
diff --git a/chrome/browser/chrome_browser_main.cc b/chrome/browser/chrome_browser_main.cc
index c3e48db67c183055ee54683f3e3ffdc41bd89c1d..4243afc4489e1d875bd5973ccb5dfeee488d7411 100644
--- a/chrome/browser/chrome_browser_main.cc
+++ b/chrome/browser/chrome_browser_main.cc
@@ -22,6 +22,7 @@
 #include "base/files/file_util.h"
 #include "base/metrics/field_trial.h"
 #include "base/metrics/histogram_macros.h"
+#include "base/metrics/user_metrics.h"
 #include "base/path_service.h"
 #include "base/profiler/scoped_profile.h"
 #include "base/profiler/scoped_tracker.h"
@@ -666,6 +667,9 @@ void ChromeBrowserMainParts::SetupMetricsAndFieldTrials() {
   // but before field trials are set up (so that client ID is available for
   // one-time randomized field trials).
 
+  base::SetRecordActionTaskRunner(
+      BrowserThread::GetMessageLoopProxyForThread(BrowserThread::UI));

[piman, 2016/04/18 21:13:08]

Should this be done in content/ ? There are tests (e.g. layout tests) and other
embedders that don't use chrome/

[beaudoin, 2016/04/19 16:57:27]

asvitkine@ for opinions.

My opinion is that other embedders and/or tests are likely to need a different
task runner and should set it up. I've done it in user_action_tester.cc using a
custom SimpleTaskRunner.

[Alexei Svitkine (slow), 2016/04/19 17:56:41]

Yeah, since this only affects cases where AddActionCallback() has been used to
set a callback, I don't think it's needed in content - since that is not
currently done in content. At least with this CL.

I guess if we do want to start using this from content in a future CL, then it
can be done at that point.

+
   // Initialize FieldTrialList to support FieldTrials that use one-time
   // randomization.
   metrics::MetricsService* metrics = browser_process_->metrics_service();