Make MessageLoopProxy::current() usable on threads that don't have MessageLoop.

base/message_loop_unittest.cc

Index: base/message_loop_unittest.cc
diff --git a/base/message_loop_unittest.cc b/base/message_loop_unittest.cc
index 15f825b7ac992eb791ecc2332819e7a03b160896..6d264fd0dd50597f781a0f6d991424ce36a5f45a 100644
--- a/base/message_loop_unittest.cc
+++ b/base/message_loop_unittest.cc
@@ -1689,3 +1689,24 @@ TEST(MessageLoopTest, DestructionObserverTest) {
   EXPECT_TRUE(task_destroyed);
   EXPECT_TRUE(destruction_observer_called);
 }
+
+// Verify that MessageLoop sets ThreadMainTaskRunner::current() and it
+// posts tasks on that message loop.
+TEST(MessageLoopTest, ThreadMainTaskRunner) {
+  MessageLoop loop;
+
+  scoped_refptr<Foo> foo(new Foo());
+  std::string a("a");
+  base::ThreadMainTaskRunner::current()->PostTask(FROM_HERE, base::Bind(
+      &Foo::Test1ConstRef, foo.get(), a));
+
+  // Post quit task;
+  MessageLoop::current()->PostTask(FROM_HERE, base::Bind(
+      &MessageLoop::Quit, base::Unretained(MessageLoop::current())));
+
+  // Now kick things off
+  MessageLoop::current()->Run();
+
+  EXPECT_EQ(foo->test_count(), 1);
+  EXPECT_EQ(foo->result(), "a");
+}