Decouple Metrics Initialization from IO Thread Initialization

components/metrics/metrics_service.cc

 // Copyright 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.
 
 //------------------------------------------------------------------------------
 // Description of the life cycle of a instance of MetricsService.
 //
 //  OVERVIEW
 //
 // A MetricsService instance is typically created at application startup.  It is
@@ skipping 518 matching lines @@
   local_state_->SetInteger(prefs::kStabilityDeferredCount, 0);
   // Note: kStabilityDiscardCount is not cleared as its intent is to measure
   // the number of times data is discarded, even across versions.
   local_state_->SetInteger(prefs::kStabilityVersionMismatchCount, 0);
 }
 
 void MetricsService::PushExternalLog(const std::string& log) {
   log_manager_.StoreLog(log, MetricsLog::ONGOING_LOG);
 }
 
-UpdateUsagePrefCallbackType MetricsService::GetDataUseForwardingCallback() {
+void MetricsService::UpdateMetricsUsagePrefs(
+    const std::string& service_name, int message_size, bool is_cellular) {

[Alexei Svitkine (slow), 2016/11/30 19:16:27]

Nit: Each param on its own line if the first param is. Or just run git cl format
which I believe will do that.

[robliao, 2016/11/30 20:33:13]

Done.

https://google.github.io/styleguide/cppguide.html#Function_Declarations_and_D...
https://google.github.io/styleguide/cppguide.html#Function_Calls
The style ruling for declarations and invocations is ...
Wrap parameter lists which do not fit on a single line as you would wrap
arguments in a function call.

Either write the call all on a single line, 
wrap the arguments at the parenthesis, or 
start the arguments on a new line indented by four spaces and continue at that 4
space indent.

In the absence of other considerations, use the minimum number of lines,
including placing multiple arguments on each line where appropriate.

One argument per line is technically a violation of the minimum space rule but
this rule is violated pretty much across Chromium. However, at the same time,
the rule need not always be followed as there is discretion allowed by the style
guide:

If there is still a case where one argument is significantly more readable on
its own line, then put it on its own line.

So basically, you're free to do what you want as long as it looks good :-)

   DCHECK(IsSingleThreaded());
-
   if (data_use_tracker_) {
-    return data_use_tracker_->GetDataUseForwardingCallback(
-        base::ThreadTaskRunnerHandle::Get());
+    data_use_tracker_->UpdateMetricsUsagePrefs(
+        service_name, message_size, is_cellular);
   }
-  return UpdateUsagePrefCallbackType();
 }
 
 void MetricsService::MergeHistogramDeltas() {
   for (MetricsProvider* provider : metrics_providers_)
     provider->MergeHistogramDeltas();
 }
 
 //------------------------------------------------------------------------------
 // private methods
 //------------------------------------------------------------------------------
@@ skipping 669 matching lines @@
                  base::Time::Now().ToTimeT());
 }
 
 void MetricsService::SkipAndDiscardUpload() {
   log_manager_.DiscardStagedLog();
   scheduler_->UploadCancelled();
   log_upload_in_progress_ = false;
 }
 
 }  // namespace metrics