Add base::ThreadTaskRunner class.

base/message_loop.cc

Index: base/message_loop.cc
diff --git a/base/message_loop.cc b/base/message_loop.cc
index f60bf69d8302a2c8122cbf26ef5948f340656178..dd8ba3ad06891fd6d2409d36c94ced6ffa7f6310 100644
--- a/base/message_loop.cc
+++ b/base/message_loop.cc
@@ -17,6 +17,7 @@
 #include "base/message_pump_default.h"
 #include "base/metrics/histogram.h"
 #include "base/third_party/dynamic_annotations/dynamic_annotations.h"
+#include "base/thread_task_runner_handle.h"
 #include "base/threading/thread_local.h"
 #include "base/time.h"
 #include "base/tracked_objects.h"
@@ -139,6 +140,8 @@ MessageLoop::MessageLoop(Type type)
   lazy_tls_ptr.Pointer()->Set(this);
 
   message_loop_proxy_ = new base::MessageLoopProxyImpl();
+  thread_task_runner_handle_.reset(
+      new base::ThreadTaskRunnerHandle(message_loop_proxy_));
 
 // TODO(rvargas): Get rid of the OS guards.
 #if defined(OS_WIN)
@@ -198,6 +201,8 @@ MessageLoop::~MessageLoop() {
   FOR_EACH_OBSERVER(DestructionObserver, destruction_observers_,
                     WillDestroyCurrentMessageLoop());
 
+  thread_task_runner_handle_.reset();

[Ryan Sleevi, 2012/05/31 19:36:41]

Not to resurrect a dead review, but when looking at this code after chatting
with Will on IRC, shouldn't this code run /after/
WillDestroyCurrentMessageLoop()?

Currently, any code that executes in WillDestroyCurrentMessageLoop() can
"safely" call MessageLoopProxy::current() and still get the current proxy (even
if their tasks will never run).

With this change, any code updated to use ThreadTaskRunnerHandle::Get(), that
runs within the context of WillDestroyCurrentMessageLoop(), will get NULL
instead. Seems like a bug?

(Or not, but I was hoping someone could comment on this)

[Sergey Ulanov, 2012/05/31 20:14:04]

This code runs only after all message loop destruction observers are notified -
see FOR_EACH_OBSERVER() two lines above.
MessageLoopProxy::WillDestroyCurrentMessageLoop() is called later, but that
shouldn't matter - MessageLoopProxy shouldn't depend on ThreadTaskRunnerHandle.

+
   // Tell the message_loop_proxy that we are dying.
   static_cast<base::MessageLoopProxyImpl*>(message_loop_proxy_.get())->
       WillDestroyCurrentMessageLoop();