Use weak_ptr in bind call to TraceLog::OnFlushTimeout

base/debug/trace_event_impl.cc

Index: base/debug/trace_event_impl.cc
diff --git a/base/debug/trace_event_impl.cc b/base/debug/trace_event_impl.cc
index db321e2bfa42c893e34acce70c37d802459c0e6f..1819d1a6dd3cbd8d7ad95651493a5fc16d99d5a1 100644
--- a/base/debug/trace_event_impl.cc
+++ b/base/debug/trace_event_impl.cc
@@ -1212,7 +1212,8 @@ TraceLog::TraceLog()
       event_callback_category_filter_(
           CategoryFilter::kDefaultCategoryFilterString),
       thread_shared_chunk_index_(0),
-      generation_(0) {
+      generation_(0),
+      weak_ptr_factory_(this) {
   // Trace is enabled or disabled on one thread while other threads are
   // accessing the enabled flag. We don't care whether edge-case events are
   // traced or not, so we allow races on the enabled flag to keep the trace
@@ -1729,7 +1730,9 @@ void TraceLog::Flush(const TraceLog::OutputCallback& cb) {
     }
     flush_message_loop_proxy_->PostDelayedTask(

[mmenke, 2014/09/12 17:47:46]

The weak pointer factory can only vend weak points on the thread the TraceLog
lives on, and its weak pointers can only be dereferenced on the same thread.

As a result, this only works if the TraceLog is created and destroyed on the
flush_message_loop_proxy_'s message loop.

The real issue is that the message loop outlives the TraceLog, which breaks the
underlying assumptions of this code.

         FROM_HERE,
-        Bind(&TraceLog::OnFlushTimeout, Unretained(this), generation),
+        Bind(&TraceLog::OnFlushTimeout,
+             weak_ptr_factory_.GetWeakPtr(),
+             generation),
         TimeDelta::FromMilliseconds(kThreadFlushTimeoutMs));
     return;
   }