memory-infra: Avoid dereferencing polling_state_ when it could be null

base/trace_event/memory_dump_scheduler.cc

Index: base/trace_event/memory_dump_scheduler.cc
diff --git a/base/trace_event/memory_dump_scheduler.cc b/base/trace_event/memory_dump_scheduler.cc
index 66ea6c9f1aeb5dd98b8af1ac43d11a26b0d025be..f63e85e148b274b788acbd8d72aefc1fdc29f7c8 100644
--- a/base/trace_event/memory_dump_scheduler.cc
+++ b/base/trace_event/memory_dump_scheduler.cc
@@ -171,7 +171,7 @@ void MemoryDumpScheduler::RequestPeriodicGlobalDump() {
 }
 
 void MemoryDumpScheduler::PollMemoryOnPollingThread() {
-  if (polling_state_->current_state != PollingTriggerState::ENABLED)
+  if (!polling_state_)

[Primiano Tucci (use gerrit), 2017/03/29 16:21:22]

I think you need both checks, i.e.
if (!polling_state_ || polling_state_->current_ctate...)

[ssid, 2017/03/29 16:41:45]

No the fix is correct as it is. As soon as disabled is set to null. I just
checked the won't condition.

[ssid, 2017/03/29 16:46:38]

Maybe a dcheck(enabled)

     return;
 
   uint64_t polled_memory = 0;