Make FML task runner methods virtual so that FXL adaptors in Fuchsia are possible. (#5921)

fml/task_runner.cc

@@ -15,9 +15,7 @@
 namespace fml {
 
 TaskRunner::TaskRunner(fml::RefPtr<MessageLoopImpl> loop)
-    : loop_(std::move(loop)) {
-  FML_CHECK(loop_);
-}
+    : loop_(std::move(loop)) {}
 
 TaskRunner::~TaskRunner() = default;
 

fml/task_runner.h

@@ -17,23 +17,24 @@ class MessageLoopImpl;
 
 class TaskRunner : public fml::RefCountedThreadSafe<TaskRunner> {
  public:
-  void PostTask(fml::closure task);
+  virtual void PostTask(fml::closure task);
 
-  void PostTaskForTime(fml::closure task, fml::TimePoint target_time);
+  virtual void PostTaskForTime(fml::closure task, fml::TimePoint target_time);
 
-  void PostDelayedTask(fml::closure task, fml::TimeDelta delay);
+  virtual void PostDelayedTask(fml::closure task, fml::TimeDelta delay);
 
-  bool RunsTasksOnCurrentThread();
+  virtual bool RunsTasksOnCurrentThread();
+
+  virtual ~TaskRunner();
 
   static void RunNowOrPostTask(fml::RefPtr<fml::TaskRunner> runner,
                                fml::closure task);
 
- private:
-  fml::RefPtr<MessageLoopImpl> loop_;
-
+ protected:
   TaskRunner(fml::RefPtr<MessageLoopImpl> loop);
 
-  ~TaskRunner();
+ private:
+  fml::RefPtr<MessageLoopImpl> loop_;
 
   FML_FRIEND_MAKE_REF_COUNTED(TaskRunner);
   FML_FRIEND_REF_COUNTED_THREAD_SAFE(TaskRunner);