memory coordinator: Add trace macros to track state changes

content/browser/memory/memory_coordinator_impl.cc

Index: content/browser/memory/memory_coordinator_impl.cc
diff --git a/content/browser/memory/memory_coordinator_impl.cc b/content/browser/memory/memory_coordinator_impl.cc
index 5fa4ea4b3b0ed221efb56ecd509975750888fd47..46eda86f00e2c09a09b38f6f734385ad0e78e914 100644
--- a/content/browser/memory/memory_coordinator_impl.cc
+++ b/content/browser/memory/memory_coordinator_impl.cc
@@ -5,6 +5,7 @@
 #include "content/browser/memory/memory_coordinator_impl.h"
 
 #include "base/threading/thread_task_runner_handle.h"
+#include "base/trace_event/trace_event.h"
 #include "content/browser/memory/memory_monitor.h"
 #include "content/public/browser/notification_service.h"
 #include "content/public/browser/notification_types.h"
@@ -196,6 +197,10 @@ void MemoryCoordinatorImpl::UpdateState() {
   }
 
   if (next_state != prev_state) {
+    TRACE_EVENT2("memory-infra", "MemoryCoordinatorImpl::UpdateState",
+                 "prev", static_cast<int32_t>(prev_state),
+                 "next", static_cast<int32_t>(next_state));

[haraken, 2016/11/01 03:58:06]

Is there any way to pass in human-readable strings to trace events?

[bashi, 2016/11/01 04:04:40]

I'm happy to add a helper function for MemoryState -> string conversion. Do we
want it?

[bashi, 2016/11/01 04:17:27]

Done.

+
     NotifyStateToClients();
     NotifyStateToChildren();
     ScheduleUpdateState(minimum_transition_period_);