Expose Thread::using_external_message_loop() to subclasses.

base/threading/thread_unittest.cc

Index: base/threading/thread_unittest.cc
diff --git a/base/threading/thread_unittest.cc b/base/threading/thread_unittest.cc
index 92ccc87d2b581b76da8e083f9dc179744cbf6c92..afb8b4a0830ec2b855219f06490290f56c93da97 100644
--- a/base/threading/thread_unittest.cc
+++ b/base/threading/thread_unittest.cc
@@ -486,6 +486,12 @@ class ExternalMessageLoopThread : public Thread {
 
   void InstallMessageLoop() { SetMessageLoop(&external_message_loop_); }
 
+  void VerifyUsingExternalMessageLoop(
+      bool expected_using_external_message_loop) {
+    EXPECT_EQ(expected_using_external_message_loop,
+              using_external_message_loop());
+  }
+
  private:
   base::MessageLoop external_message_loop_;
 
@@ -498,10 +504,12 @@ TEST_F(ThreadTest, ExternalMessageLoop) {
   ExternalMessageLoopThread a;
   EXPECT_FALSE(a.message_loop());
   EXPECT_FALSE(a.IsRunning());
+  a.VerifyUsingExternalMessageLoop(false);
 
   a.InstallMessageLoop();
   EXPECT_TRUE(a.message_loop());
   EXPECT_TRUE(a.IsRunning());
+  a.VerifyUsingExternalMessageLoop(true);
 
   bool ran = false;
   a.task_runner()->PostTask(
@@ -512,6 +520,7 @@ TEST_F(ThreadTest, ExternalMessageLoop) {
   a.Stop();
   EXPECT_FALSE(a.message_loop());
   EXPECT_FALSE(a.IsRunning());
+  a.VerifyUsingExternalMessageLoop(true);
 
   // Confirm that running any remaining tasks posted from Stop() goes smoothly
   // (e.g. https://codereview.chromium.org/2135413003/#ps300001 crashed if