Ensure BrowserThread::CurrentlyOn is correct through MessageLoop teardown

content/browser/browser_thread_unittest.cc

Index: content/browser/browser_thread_unittest.cc
diff --git a/content/browser/browser_thread_unittest.cc b/content/browser/browser_thread_unittest.cc
index f3f37952ff73ea072dfd12e08bb9b0ff08bbaa18..0538819fa3d3bcecfb49604f1f679a9a83b99c70 100644
--- a/content/browser/browser_thread_unittest.cc
+++ b/content/browser/browser_thread_unittest.cc
@@ -7,9 +7,11 @@
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #include "base/location.h"
+#include "base/message_loop/message_loop.h"
 #include "base/run_loop.h"
 #include "base/sequenced_task_runner_helpers.h"
 #include "base/single_thread_task_runner.h"
+#include "base/threading/thread_task_runner_handle.h"
 #include "content/browser/browser_thread_impl.h"
 #include "content/public/test/test_browser_thread.h"
 #include "testing/gtest/include/gtest/gtest.h"
@@ -25,6 +27,10 @@ class BrowserThreadTest : public testing::Test {
                                   base::MessageLoop::QuitWhenIdleClosure());
   }
 
+  void StopFileThread() {
+    file_thread_->Stop();
+  }
+
  protected:
   void SetUp() override {
     ui_thread_.reset(new BrowserThreadImpl(BrowserThread::UI));
@@ -35,7 +41,7 @@ class BrowserThreadTest : public testing::Test {
 
   void TearDown() override {
     ui_thread_->Stop();
-    file_thread_->Stop();
+    StopFileThread();
   }
 
   static void BasicFunction(base::MessageLoop* message_loop) {
@@ -72,6 +78,44 @@ class BrowserThreadTest : public testing::Test {
   mutable base::MessageLoop loop_;
 };
 
+class FileThreadDestructionObserver
+    : public base::MessageLoop::DestructionObserver {
+ public:
+  explicit FileThreadDestructionObserver(bool* did_shutdown,
+                                         const base::Closure& callback)
+      : callback_task_runner_(base::ThreadTaskRunnerHandle::Get()),
+        callback_(callback),
+        file_task_runner_(
+            BrowserThread::GetTaskRunnerForThread(BrowserThread::FILE)),
+        did_shutdown_(did_shutdown) {
+    BrowserThread::GetTaskRunnerForThread(BrowserThread::FILE)->PostTask(
+        FROM_HERE, base::Bind(&Watch, this));
+  }
+
+ private:
+  static void Watch(FileThreadDestructionObserver* observer) {
+    base::MessageLoop::current()->AddDestructionObserver(observer);
+  }
+
+  // base::MessageLoop::DestructionObserver:
+  void WillDestroyCurrentMessageLoop() override {
+    // Ensure that even during MessageLoop teardown the BrowserThread ID is
+    // correctly associated with this thread and the BrowserThreadTaskRunner
+    // knows it's on the right thread.
+    EXPECT_TRUE(BrowserThread::CurrentlyOn(BrowserThread::FILE));
+    EXPECT_TRUE(file_task_runner_->BelongsToCurrentThread());
+
+    base::MessageLoop::current()->RemoveDestructionObserver(this);
+    *did_shutdown_ = true;
+    callback_task_runner_->PostTask(FROM_HERE, callback_);
+  }
+
+  const scoped_refptr<base::SingleThreadTaskRunner> callback_task_runner_;
+  const base::Closure callback_;
+  const scoped_refptr<base::SingleThreadTaskRunner> file_task_runner_;
+  bool* did_shutdown_;
+};
+
 TEST_F(BrowserThreadTest, PostTask) {
   BrowserThread::PostTask(
       BrowserThread::FILE,
@@ -118,4 +162,16 @@ TEST_F(BrowserThreadTest, PostTaskAndReply) {
   base::RunLoop().Run();
 }
 
+TEST_F(BrowserThreadTest, RunsTasksOnCurrentThreadDuringShutdown) {
+  bool did_shutdown = false;
+  base::RunLoop loop;
+  FileThreadDestructionObserver observer(&did_shutdown, loop.QuitClosure());
+  base::ThreadTaskRunnerHandle::Get()->PostTask(
+      FROM_HERE,
+      base::Bind(&BrowserThreadTest::StopFileThread, base::Unretained(this)));
+  loop.Run();
+
+  EXPECT_TRUE(did_shutdown);
+}
+
 }  // namespace content