base: Make it possible to replace the MessageLoop's task runner

base/message_loop/message_loop_unittest.cc

Index: base/message_loop/message_loop_unittest.cc
diff --git a/base/message_loop/message_loop_unittest.cc b/base/message_loop/message_loop_unittest.cc
index 48c82c4792b51a5e0d67e9ca7737bd24a885e4bb..9c1701756882febefde91d667e3b38312da8cb11 100644
--- a/base/message_loop/message_loop_unittest.cc
+++ b/base/message_loop/message_loop_unittest.cc
@@ -15,6 +15,7 @@
 #include "base/posix/eintr_wrapper.h"
 #include "base/run_loop.h"
 #include "base/synchronization/waitable_event.h"
+#include "base/test/test_simple_task_runner.h"
 #include "base/thread_task_runner_handle.h"
 #include "base/threading/platform_thread.h"
 #include "base/threading/thread.h"
@@ -1011,4 +1012,26 @@ TEST(MessageLoopTest, AlwaysHaveUserMessageWhenNesting) {
 }
 #endif  // defined(OS_WIN)
 
+TEST(MessageLoopTest, SetTaskRunner) {
+  MessageLoop loop;
+  scoped_refptr<SingleThreadTaskRunner> new_runner(new TestSimpleTaskRunner());
+
+  loop.SetTaskRunner(new_runner);
+  EXPECT_EQ(new_runner, loop.task_runner());
+  EXPECT_EQ(new_runner, ThreadTaskRunnerHandle::Get());
+}
+
+TEST(MessageLoopTest, OriginalRunnerWorks) {
+  MessageLoop loop;
+  scoped_refptr<SingleThreadTaskRunner> new_runner(new TestSimpleTaskRunner());
+  scoped_refptr<SingleThreadTaskRunner> original_runner(loop.task_runner());
+  loop.SetTaskRunner(new_runner);
+
+  scoped_refptr<Foo> foo(new Foo());
+  original_runner->PostTask(FROM_HERE,
+                            Bind(&Foo::Test1ConstRef, foo.get(), "a"));
+  loop.RunUntilIdle();
+  EXPECT_EQ(1, foo->test_count());
+}
+
 }  // namespace base