memory-infra: Never kill memory-infra background thread

base/trace_event/memory_dump_manager.h

 // 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.
 
 #ifndef BASE_TRACE_EVENT_MEMORY_DUMP_MANAGER_H_
 #define BASE_TRACE_EVENT_MEMORY_DUMP_MANAGER_H_
 
 #include <stdint.h>
 
 #include <map>
@@ skipping 227 matching lines @@
 
   MemoryDumpManager();
   virtual ~MemoryDumpManager();
 
   static void SetInstanceForTesting(MemoryDumpManager* instance);
   static uint32_t GetDumpsSumKb(const std::string&, const ProcessMemoryDump*);
 
   void FinalizeDumpAndAddToTrace(
       std::unique_ptr<ProcessMemoryDumpAsyncState> pmd_async_state);
 
+  // Lazily initializes dump_thread_ and returns its TaskRunner.
+  scoped_refptr<base::SingleThreadTaskRunner> GetTaskRunner();

[Primiano Tucci (use gerrit), 2017/04/24 15:30:58]

I'd call this GetOrCreateBgTaskRunnerLocked()
"GetOrCreate", to reflect the fact that will lazily initialize a new one.
"Locked" to reflect the locking need.
"Bg" to reflect that this is our "background" thread.

Also, just a minor documentation thing. I think we could return a
SequencedTaskRunner here.
Nothing will change in practice in the .cc file (a SingleThread task runner is
also sequenced). Is just about the recent discussions on chromium-dev.
"SingleThread" should be used only in the cases where we actually need thread
affinity (read: we rely on a TLS slot, which IIRC is not the case here).
In all other cases where we just need sequencing, STR is the way to go.

[hjd, 2017/04/24 16:27:59]

Done.

+
   // Internal, used only by MemoryDumpManagerDelegate.
   // Creates a memory dump for the current process and appends it to the trace.
   // |callback| will be invoked asynchronously upon completion on the same
   // thread on which CreateProcessDump() was called.
   void CreateProcessDump(const MemoryDumpRequestArgs& args,
                          const ProcessMemoryDumpCallback& callback);
 
   // Calls InvokeOnMemoryDump() for the next MDP on the task runner specified by
   // the MDP while registration. On failure to do so, skips and continues to
   // next MDP.
@@ skipping 81 matching lines @@
   }
 
  private:
   DISALLOW_COPY_AND_ASSIGN(MemoryDumpManagerDelegate);
 };
 
 }  // namespace trace_event
 }  // namespace base
 
 #endif  // BASE_TRACE_EVENT_MEMORY_DUMP_MANAGER_H_