Cancel a task associated to TaskHandle when the TaskHandle is overridden

third_party/WebKit/Source/platform/WebTaskRunnerTest.cpp

 // Copyright 2016 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 "platform/WebTaskRunner.h"
 
 #include "platform/scheduler/test/fake_web_task_runner.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace blink {
@@ skipping 45 matching lines @@
   {
     count = 0;
     TaskHandle handle2 = taskRunner.postCancellableTask(
         BLINK_FROM_HERE, WTF::bind(&increment, WTF::unretained(&count)));
     EXPECT_TRUE(handle2.isActive());
   }
   EXPECT_EQ(0, count);
   taskRunner.runUntilIdle();
   EXPECT_EQ(0, count);
 
+  // The task should be cancelled when another TaskHandle is assigned on it.
+  count = 0;
+  handle = taskRunner.postCancellableTask(
+      BLINK_FROM_HERE, WTF::bind(&increment, WTF::unretained(&count)));
+  handle = taskRunner.postCancellableTask(BLINK_FROM_HERE, WTF::bind([] {}));
+  EXPECT_EQ(0, count);
+  taskRunner.runUntilIdle();
+  EXPECT_EQ(0, count);
+
+  // Self assign should be nop.
+  count = 0;
+  handle = taskRunner.postCancellableTask(
+      BLINK_FROM_HERE, WTF::bind(&increment, WTF::unretained(&count)));
+#if COMPILER(CLANG)
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wself-move"
+  handle = std::move(handle);
+#pragma GCC diagnostic pop
+#else
+  handle = std::move(handle);
+#endif  // COMPILER(CLANG)
+  EXPECT_EQ(0, count);
+  taskRunner.runUntilIdle();
+  EXPECT_EQ(1, count);
+
   // handle->isActive() should switch to false before the task starts running.
   bool isActive = false;
   handle = taskRunner.postCancellableTask(
       BLINK_FROM_HERE, WTF::bind(&getIsActive, WTF::unretained(&isActive),
                                  WTF::unretained(&handle)));
   EXPECT_TRUE(handle.isActive());
   taskRunner.runUntilIdle();
   EXPECT_FALSE(isActive);
   EXPECT_FALSE(handle.isActive());
 }
 
 }  // namespace blink