Add trace code to track all posted tasks in message_loop.

base/debug/trace_event.cc

Index: base/debug/trace_event.cc
diff --git a/base/debug/trace_event.cc b/base/debug/trace_event.cc
index 8eb774e5b5cebd74f82770a1539086d21f54b5f6..2cce7140887f10e254bb4cf9b52d1bdcdc574d76 100644
--- a/base/debug/trace_event.cc
+++ b/base/debug/trace_event.cc
@@ -20,6 +20,14 @@
 
 #define USE_UNRELIABLE_NOW
 
+class DeleteTraceLogForTesting {
+ public:
+  static void Delete() {
+    Singleton<base::debug::TraceLog,
+              StaticMemorySingletonTraits<base::debug::TraceLog> >::OnExit(0);
+  }
+};
+
 namespace base {
 namespace debug {
 
@@ -489,6 +497,10 @@ void TraceLog::AddCurrentMetadataEvents() {
   }
 }
 
+void TraceLog::DeleteForTesting() {
+  DeleteTraceLogForTesting::Delete();
+}
+
 void TraceLog::Resurrect() {
   StaticMemorySingletonTraits<TraceLog>::Resurrect();
 }