memory-infra: Remove is_enabled_ from MDM

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 03192bfa91efd9521ee335755c46a61ec668d278..9b2aaae8ffa2a9372eb6ca03fabaa75bf9a81c67 100644
--- a/base/trace_event/memory_dump_manager.h
+++ b/base/trace_event/memory_dump_manager.h
@@ -307,10 +307,6 @@ class BASE_EXPORT MemoryDumpManager {
   // disabling logging while dumping on another thread.
   Lock lock_;
 
-  // 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 is_enabled_;
-
   // Thread used for MemoryDumpProviders which don't specify a task runner
   // affinity.
   std::unique_ptr<Thread> dump_thread_;