base: Remove most uses of MessageLoopProxy

base/trace_event/trace_event_impl.h

Index: base/trace_event/trace_event_impl.h
diff --git a/base/trace_event/trace_event_impl.h b/base/trace_event/trace_event_impl.h
index 33a85c9b6ce854f4e6b6cde748fe6abca8a015d2..50d33ca7da9129a62f1a4518381bb6bce4898033 100644
--- a/base/trace_event/trace_event_impl.h
+++ b/base/trace_event/trace_event_impl.h
@@ -18,6 +18,7 @@
 #include "base/memory/ref_counted_memory.h"
 #include "base/memory/scoped_vector.h"
 #include "base/observer_list.h"
+#include "base/single_thread_task_runner.h"
 #include "base/strings/string_util.h"
 #include "base/synchronization/condition_variable.h"
 #include "base/synchronization/lock.h"
@@ -798,8 +799,8 @@ class BASE_EXPORT TraceLog {
   ThreadLocalBoolean thread_is_in_trace_event_;
 
   // Contains the message loops of threads that have had at least one event
-  // added into the local event buffer. Not using MessageLoopProxy because we
-  // need to know the life time of the message loops.
+  // added into the local event buffer. Not using SingleThreadTaskRunner

[danakj, 2015/04/21 20:16:31]

Can you verify that this comment is as correct as it was before? Lifetimes of
STTR and MessageLoop are not clear to me. 

[Sami, 2015/04/23 17:48:25]

It's still accurate: the reason concrete MessageLoops are needed here as opposed
to MLP/STTR is that you can only attach a destruction observer to a MessageLoop.
The change from MLP to STTR doesn't affect that since the ThreadTaskRunnerHandle
"lifetime" is the same as an MLP (I say "lifetime" because both are refcounted
so you can hang onto them for as long as you want).

+  // because we need to know the life time of the message loops.
   hash_set<MessageLoop*> thread_message_loops_;
 
   // For events which can't be added into the thread local buffer, e.g. events
@@ -809,7 +810,7 @@ class BASE_EXPORT TraceLog {
 
   // Set when asynchronous Flush is in progress.
   OutputCallback flush_output_callback_;
-  scoped_refptr<MessageLoopProxy> flush_message_loop_proxy_;
+  scoped_refptr<SingleThreadTaskRunner> flush_task_runner_;
   subtle::AtomicWord generation_;
   bool use_worker_thread_;