[Cleanup] Pass a callback as a function argument, rather than caching…

… it as a class variable.

This clarifies its lifetime and usage expectations.

BUG=none
TEST=none
R=asvitkine@chromium.org

Review URL: https://codereview.chromium.org/1302253002

Cr-Commit-Position: refs/heads/master@{#345100}

components/metrics/drive_metrics_provider.cc

@@ -6,6 +6,7 @@
 
 #include "base/base_paths.h"
 #include "base/bind.h"
+#include "base/callback.h"
 #include "base/files/file_path.h"
 #include "base/location.h"
 #include "base/logging.h"
@@ -33,15 +34,13 @@ void DriveMetricsProvider::ProvideSystemProfileMetrics(
                    hardware->mutable_user_data_drive());
 }
 
-void DriveMetricsProvider::GetDriveMetrics(const base::Closure& done) {
-  got_metrics_callback_ = done;
-
+void DriveMetricsProvider::GetDriveMetrics(const base::Closure& done_callback) {
   base::PostTaskAndReplyWithResult(
       file_thread_.get(), FROM_HERE,
       base::Bind(&DriveMetricsProvider::GetDriveMetricsOnFileThread,
                  local_state_path_key_),
       base::Bind(&DriveMetricsProvider::GotDriveMetrics,
-                 weak_ptr_factory_.GetWeakPtr()));
+                 weak_ptr_factory_.GetWeakPtr(), done_callback));
 }
 
 DriveMetricsProvider::SeekPenaltyResponse::SeekPenaltyResponse()
@@ -81,10 +80,11 @@ void DriveMetricsProvider::QuerySeekPenalty(
 }
 
 void DriveMetricsProvider::GotDriveMetrics(
+    const base::Closure& done_callback,
     const DriveMetricsProvider::DriveMetrics& metrics) {
   DCHECK(thread_checker_.CalledOnValidThread());
   metrics_ = metrics;
-  got_metrics_callback_.Run();
+  done_callback.Run();
 }
 
 void DriveMetricsProvider::FillDriveMetrics(

components/metrics/drive_metrics_provider.h

@@ -5,7 +5,7 @@
 #ifndef COMPONENTS_METRICS_DRIVE_METRICS_PROVIDER_H_
 #define COMPONENTS_METRICS_DRIVE_METRICS_PROVIDER_H_
 
-#include "base/callback.h"
+#include "base/callback_forward.h"
 #include "base/gtest_prod_util.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
@@ -37,7 +37,7 @@ class DriveMetricsProvider : public metrics::MetricsProvider {
       metrics::SystemProfileProto* system_profile_proto) override;
 
   // Called to start gathering metrics.
-  void GetDriveMetrics(const base::Closure& done);
+  void GetDriveMetrics(const base::Closure& done_callback);
 
  private:
   FRIEND_TEST_ALL_PREFIXES(DriveMetricsProviderTest, HasSeekPenalty);
@@ -69,7 +69,10 @@ class DriveMetricsProvider : public metrics::MetricsProvider {
                                SeekPenaltyResponse* response);
 
   // Called when metrics are done being gathered from the FILE thread.
-  void GotDriveMetrics(const DriveMetrics& metrics);
+  // |done_callback| is the callback that should be called once all metrics are
+  // gathered.
+  void GotDriveMetrics(const base::Closure& done_callback,
+                       const DriveMetrics& metrics);
 
   // Fills |drive| with information from successful |response|s.
   void FillDriveMetrics(const SeekPenaltyResponse& response,
@@ -86,9 +89,6 @@ class DriveMetricsProvider : public metrics::MetricsProvider {
   // Information gathered about various important drives.
   DriveMetrics metrics_;
 
-  // Called when metrics are done being collected.
-  base::Closure got_metrics_callback_;
-
   base::ThreadChecker thread_checker_;
   base::WeakPtrFactory<DriveMetricsProvider> weak_ptr_factory_;