Decouple Metrics Initialization from IO Thread Initialization

components/metrics/metrics_service.cc

Index: components/metrics/metrics_service.cc
diff --git a/components/metrics/metrics_service.cc b/components/metrics/metrics_service.cc
index b896440857adfc4bfc2e4940519f158a85330a87..13768db5c581fdd4113f7758ea3a6f54fc4044e6 100644
--- a/components/metrics/metrics_service.cc
+++ b/components/metrics/metrics_service.cc
@@ -536,14 +536,13 @@ 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() {