Make ExternalDataUseReporter independent of other data use classes

chrome/browser/android/data_usage/external_data_use_reporter_unittest.cc

 // Copyright 2016 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.
 
 #include "chrome/browser/android/data_usage/external_data_use_reporter.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <map>
@@ skipping 124 matching lines @@
 
   ExternalDataUseObserver* external_data_use_observer() const {
     return external_data_use_observer_.get();
   }
 
   ExternalDataUseReporter* external_data_use_reporter() const {
     return external_data_use_observer_->GetExternalDataUseReporterForTesting();
   }
 
   DataUseTabModel* data_use_tab_model() const {
-    return external_data_use_reporter()->data_use_tab_model_;
+    return external_data_use_observer()->GetDataUseTabModel();
   }
 
   const ExternalDataUseReporter::DataUseReports& buffered_data_reports() const {
     return external_data_use_reporter()->buffered_data_reports_;
   }
 
   int64_t default_upload_bytes() const { return 1; }
 
   int64_t default_download_bytes() const {
     return external_data_use_reporter()->data_use_report_min_bytes_;
@@ skipping 391 matching lines @@
   EXPECT_EQ(
       base::TimeDelta::FromMilliseconds(kDefaultMaxDataReportSubmitWaitMsec),
       external_data_use_reporter()->data_report_submit_timeout_);
   EXPECT_EQ(kDataUseReportMinBytes,
             external_data_use_reporter()->data_use_report_min_bytes_);
 }
 
 }  // namespace android
 
 }  // namespace chrome