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

base/trace_event/memory_dump_manager.h

Index: base/trace_event/memory_dump_manager.h
diff --git a/base/trace_event/memory_dump_manager.h b/base/trace_event/memory_dump_manager.h
index 79e8dfbf4b8d01a480a5dbe394f8ea980b5420a8..0b253f2436a0286c6e8e65d57e66c14e4999a7e3 100644
--- a/base/trace_event/memory_dump_manager.h
+++ b/base/trace_event/memory_dump_manager.h
@@ -370,9 +370,6 @@ class BASE_EXPORT MemoryDumpManager : public TraceLog::EnabledStateObserver {
   // dump_providers_enabled_ list) when tracing is not enabled.
   subtle::AtomicWord memory_tracing_enabled_;
 
-  // For triggering memory dumps.
-  std::unique_ptr<MemoryDumpScheduler> dump_scheduler_;
-
   // Thread used for MemoryDumpProviders which don't specify a task runner
   // affinity.
   std::unique_ptr<Thread> dump_thread_;