Fix race condition when dump providers invoked within destroyed state

base/trace_event/memory_dump_manager_unittest.cc

Index: base/trace_event/memory_dump_manager_unittest.cc
diff --git a/base/trace_event/memory_dump_manager_unittest.cc b/base/trace_event/memory_dump_manager_unittest.cc
index 2461e616790476de6ab95ef14a8ddc2695b21d01..d6809366e3ea101becac22d5fcdc7cdc39051ae3 100644
--- a/base/trace_event/memory_dump_manager_unittest.cc
+++ b/base/trace_event/memory_dump_manager_unittest.cc
@@ -938,8 +938,11 @@ TEST_F(MemoryDumpManagerTest, DisableTracingRightBeforeStartOfDump) {
   base::WaitableEvent tracing_disabled_event(false, false);
   InitializeMemoryDumpManager(false /* is_coordinator */);
 
+  auto thread = WrapUnique(new Thread("test thread"));

[Primiano Tucci (use gerrit), 2016/04/13 17:08:41]

I think we don't allow yet auto with WrapUnique. 
Also, there should be no need of WrapUnique here, just:
std::unique_ptr<Thread> thread(new Thread(...)) right?

[kraynov, 2016/04/13 17:17:41]

Acknowledged.

+  thread->Start();
+
   MockMemoryDumpProvider mdp;
-  RegisterDumpProvider(&mdp);
+  RegisterDumpProvider(&mdp, thread->task_runner(), kDefaultOptions);

[Primiano Tucci (use gerrit), 2016/04/13 17:08:41]

hmm here you are overriding the previous behavior. 
I would much rather add two mdp, one not bound to any thread and one bound to
|thread| here.

[kraynov, 2016/04/13 17:17:41]

Acknowledged.

   EnableTracingWithLegacyCategories(MemoryDumpManager::kTraceCategory);
 
   EXPECT_CALL(*delegate_, RequestGlobalMemoryDump(_, _))
@@ -949,6 +952,10 @@ TEST_F(MemoryDumpManagerTest, DisableTracingRightBeforeStartOfDump) {
         delegate_->CreateProcessDump(args, callback);
       }));
 
+  // If tracing is disabled for current session CreateProcessDump() should NOT
+  // request dumps from providers. Real-world regression: crbug.com/600570 .
+  EXPECT_CALL(mdp, OnMemoryDump(_, _)).Times(0);
+
   last_callback_success_ = true;
   RequestGlobalDumpAndWait(MemoryDumpType::EXPLICITLY_TRIGGERED,
                            MemoryDumpLevelOfDetail::DETAILED);