[memory-infra] Make MemoryDumpScheduler non-thread safe singleton

base/trace_event/memory_dump_manager_unittest.cc

 // Copyright 2015 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 "base/trace_event/memory_dump_manager.h"
 
 #include <stdint.h>
 
 #include <memory>
 #include <vector>
@@ skipping 257 matching lines @@
   }
 
   void EnableTracingWithTraceConfig(const std::string& trace_config) {
     TraceLog::GetInstance()->SetEnabled(TraceConfig(trace_config),
                                         TraceLog::RECORDING_MODE);
   }
 
   void DisableTracing() { TraceLog::GetInstance()->SetDisabled(); }
 
   bool IsPeriodicDumpingEnabled() const {
-    return mdm_->dump_scheduler_->IsPeriodicTimerRunningForTesting();
+    return MemoryDumpScheduler::GetInstance()
+        ->IsPeriodicTimerRunningForTesting();
   }
 
   int GetMaxConsecutiveFailuresCount() const {
     return MemoryDumpManager::kMaxConsecutiveFailuresCount;
   }
 
   const MemoryDumpProvider::Options kDefaultOptions;
   std::unique_ptr<MemoryDumpManager> mdm_;
   MemoryDumpManagerDelegateForTesting* delegate_;
   bool last_callback_success_;
@@ skipping 997 matching lines @@
   thread.Start();
   RegisterDumpProvider(&mdp1, thread.task_runner(), kDefaultOptions,
                        "BlacklistTestDumpProvider");
   // Unregistering on wrong thread should not crash.
   mdm_->UnregisterDumpProvider(&mdp1);
   thread.Stop();
 }
 
 }  // namespace trace_event
 }  // namespace base