Fixing race between ~AsyncInvoker and ~AsyncClosure, using ref-counting.

webrtc/rtc_base/asyncinvoker-inl.h

Index: webrtc/rtc_base/asyncinvoker-inl.h
diff --git a/webrtc/rtc_base/asyncinvoker-inl.h b/webrtc/rtc_base/asyncinvoker-inl.h
index 5b2cf4e250093d9629f9767ede10477b4272ad28..23e75956369eb4b7c4fe7e849270a73e6ef7115c 100644
--- a/webrtc/rtc_base/asyncinvoker-inl.h
+++ b/webrtc/rtc_base/asyncinvoker-inl.h
@@ -14,7 +14,10 @@
 #include "webrtc/rtc_base/atomicops.h"
 #include "webrtc/rtc_base/bind.h"
 #include "webrtc/rtc_base/criticalsection.h"
+#include "webrtc/rtc_base/event.h"
 #include "webrtc/rtc_base/messagehandler.h"
+#include "webrtc/rtc_base/refcountedobject.h"
+#include "webrtc/rtc_base/scoped_ref_ptr.h"
 #include "webrtc/rtc_base/sigslot.h"
 #include "webrtc/rtc_base/thread.h"
 #include "webrtc/rtc_base/thread_annotations.h"
@@ -27,7 +30,7 @@ class AsyncInvoker;
 // on the calling thread if necessary.
 class AsyncClosure {
  public:
-  explicit AsyncClosure(AsyncInvoker* invoker) : invoker_(invoker) {}
+  explicit AsyncClosure(AsyncInvoker* invoker);
   virtual ~AsyncClosure();
   // Runs the asynchronous task, and triggers a callback to the calling
   // thread if needed. Should be called from the target thread.
@@ -35,6 +38,11 @@ class AsyncClosure {
 
  protected:
   AsyncInvoker* invoker_;
+  // Reference counted so that if the AsyncInvoker destructor finishes before
+  // an AsyncClosure's destructor that's about to call
+  // "invocation_complete_->Set()", it's not dereferenced after being
+  // destroyed.
+  scoped_refptr<RefCountedObject<Event>> invocation_complete_;
 };
 
 // Simple closure that doesn't trigger a callback for the calling thread.