[tracing] Fix MemoryDumpManager periodic scheduler and improve tests

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 305ec5980767c0c9de9d70029b739340fdcc9cb0..760ad7b871de3c76176ee71203beb1ec960729f5 100644
--- a/base/trace_event/memory_dump_manager.h
+++ b/base/trace_event/memory_dump_manager.h
@@ -92,9 +92,10 @@ class BASE_EXPORT MemoryDumpManager : public TraceLog::EnabledStateObserver {
 
   // Returns the name for a the allocated_objects dump. Use this to declare
   // suballocator dumps from other dump providers.
-  // It should not return nullptr after the manager has been initialized.
+  // It will return nullptr if there is no dump provider for the system
+  // allocator registered (which is currently the case for Mac OS).
   const char* system_allocator_pool_name() const {
-    return system_allocator_pool_name_;
+    return kSystemAllocatorPoolName;
   };
 
   // Tells the initialization phase to skip scheduling periodic memory dumps.
@@ -174,6 +175,7 @@ class BASE_EXPORT MemoryDumpManager : public TraceLog::EnabledStateObserver {
   };
 
   static const int kMaxConsecutiveFailuresCount;
+  static const char* const kSystemAllocatorPoolName;
 
   MemoryDumpManager();
   ~MemoryDumpManager() override;
@@ -221,9 +223,6 @@ class BASE_EXPORT MemoryDumpManager : public TraceLog::EnabledStateObserver {
   // expected to be valid only when tracing is enabled.
   uint64 tracing_process_id_;
 
-  // Name of the allocated_objects dump.
-  const char* system_allocator_pool_name_;
-
   // Skips the auto-registration of the core dumpers during Initialize().
   bool skip_core_dumpers_auto_registration_for_testing_;