memory-infra: Never kill memory-infra background thread

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 7d35ca5cd2f51685e0c0f4a25685ef98354ef88b..8cf8cd75a435634b2801ae34c080a9fab762d20e 100644
--- a/base/trace_event/memory_dump_manager.h
+++ b/base/trace_event/memory_dump_manager.h
@@ -34,6 +34,7 @@ class ProcessLocalDumpManagerImplTest;
 
 namespace base {
 
+class SequencedTaskRunner;
 class SingleThreadTaskRunner;
 class Thread;
 
@@ -198,7 +199,7 @@ class BASE_EXPORT MemoryDumpManager {
         const MemoryDumpProviderInfo::OrderedSet& dump_providers,
         scoped_refptr<MemoryDumpSessionState> session_state,
         ProcessMemoryDumpCallback callback,
-        scoped_refptr<SingleThreadTaskRunner> dump_thread_task_runner);
+        scoped_refptr<SequencedTaskRunner> dump_thread_task_runner);
     ~ProcessMemoryDumpAsyncState();
 
     // Gets or creates the memory dump container for the given target process.
@@ -239,7 +240,7 @@ class BASE_EXPORT MemoryDumpManager {
     // as a separate variable as it needs to be accessed by arbitrary dumpers'
     // threads outside of the lock_ to avoid races when disabling tracing.
     // It is immutable for all the duration of a tracing session.
-    const scoped_refptr<SingleThreadTaskRunner> dump_thread_task_runner;
+    const scoped_refptr<SequencedTaskRunner> dump_thread_task_runner;
 
    private:
     DISALLOW_COPY_AND_ASSIGN(ProcessMemoryDumpAsyncState);
@@ -257,6 +258,9 @@ class BASE_EXPORT MemoryDumpManager {
   void FinalizeDumpAndAddToTrace(
       std::unique_ptr<ProcessMemoryDumpAsyncState> pmd_async_state);
 
+  // Lazily initializes dump_thread_ and returns its TaskRunner.
+  scoped_refptr<base::SequencedTaskRunner> GetOrCreateBgTaskRunnerLocked();
+
   // 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.
@@ -310,7 +314,7 @@ class BASE_EXPORT MemoryDumpManager {
 
   // Optimization to avoid attempting any memory dump (i.e. to not walk an empty
   // dump_providers_enabled_ list) when tracing is not enabled.
-  subtle::AtomicWord memory_tracing_enabled_;
+  subtle::AtomicWord is_enabled_;
 
   // Thread used for MemoryDumpProviders which don't specify a task runner
   // affinity.