Fix handle_watcher when start is called twice on the same handle.

mojo/common/handle_watcher_unittest.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "mojo/common/handle_watcher.h"
 
 #include <string>
 
 #include "base/at_exit.h"
 #include "base/auto_reset.h"
@@ skipping 262 matching lines @@
   EXPECT_FALSE(callback_helper2.got_callback());
 
   // Write to 1 and make sure it's notified.
   EXPECT_TRUE(mojo::test::WriteTextMessage(test_pipe1.handle1.get(),
                                            std::string()));
   callback_helper1.RunUntilGotCallback();
   EXPECT_TRUE(callback_helper1.got_callback());
   EXPECT_FALSE(callback_helper2.got_callback());
 }
 
+// Verifies Start() invoked a second time on the same handle works.
+TEST_P(HandleWatcherTest, RestartOnSameHandle) {
+  MessagePipe test_pipe;
+  CallbackHelper callback_helper;
+  ASSERT_TRUE(test_pipe.handle0.is_valid());
+
+  HandleWatcher watcher;
+  callback_helper.Start(&watcher, test_pipe.handle0.get());
+  RunUntilIdle();
+  EXPECT_FALSE(callback_helper.got_callback());
+
+  callback_helper.Start(&watcher, test_pipe.handle0.get());
+  RunUntilIdle();
+  EXPECT_FALSE(callback_helper.got_callback());
+}
+
 // Verifies deadline is honored.
 TEST_P(HandleWatcherTest, Deadline) {
   InstallTickClock();
 
   MessagePipe test_pipe1;
   MessagePipe test_pipe2;
   MessagePipe test_pipe3;
   CallbackHelper callback_helper1;
   CallbackHelper callback_helper2;
   CallbackHelper callback_helper3;
@@ skipping 165 matching lines @@
                               message_loop.task_runner(),
                               &run_loop, &threads_active_counter));
   }
   run_loop.Run();
   ASSERT_EQ(0, threads_active_counter);
 }
 
 }  // namespace test
 }  // namespace common
 }  // namespace mojo