Allow ObjectWatcher to be used from sequenced tasks.

base/win/object_watcher.h

Index: base/win/object_watcher.h
diff --git a/base/win/object_watcher.h b/base/win/object_watcher.h
index a2821c114f18279a5cc4c9b57d77d23cfd35439f..67a1e26c76cd1665b700f896075777d4c66abe58 100644
--- a/base/win/object_watcher.h
+++ b/base/win/object_watcher.h
@@ -12,7 +12,7 @@
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/weak_ptr.h"
-#include "base/single_thread_task_runner.h"
+#include "base/sequenced_task_runner.h"
 
 namespace base {
 namespace win {
@@ -20,7 +20,7 @@ namespace win {
 // A class that provides a means to asynchronously wait for a Windows object to
 // become signaled.  It is an abstraction around RegisterWaitForSingleObject
 // that provides a notification callback, OnObjectSignaled, that runs back on
-// the origin thread (i.e., the thread that called StartWatching).
+// the origin sequence (i.e., the sequence that called StartWatching).
 //
 // This class acts like a smart pointer such that when it goes out-of-scope,
 // UnregisterWaitEx is automatically called, and any in-flight notification is
@@ -48,14 +48,13 @@ namespace win {
 // still called after (but not necessarily immediately after) watch is started.
 //
 // NOTE: Except for the constructor, all public methods of this class must be
-// called on the same thread. A ThreadTaskRunnerHandle must be set on that
-// thread.
+// called in sequence, in a scope where SequencedTaskRunnerHandle::IsSet().
 class BASE_EXPORT ObjectWatcher {
  public:
   class BASE_EXPORT Delegate {
    public:
     virtual ~Delegate() {}
-    // Called from the thread that started the watch when a signaled object is
+    // Called from the sequence that started the watch when a signaled object is
     // detected. To continue watching the object, StartWatching must be called
     // again.
     virtual void OnObjectSignaled(HANDLE object) = 0;
@@ -64,16 +63,16 @@ class BASE_EXPORT ObjectWatcher {
   ObjectWatcher();
   ~ObjectWatcher();
 
-  // When the object is signaled, the given delegate is notified on the thread
+  // When the object is signaled, the given delegate is notified on the sequence
   // where StartWatchingOnce is called. The ObjectWatcher is not responsible for
   // deleting the delegate.
   // Returns whether watching was successfully initiated.
   bool StartWatchingOnce(HANDLE object, Delegate* delegate);
 
-  // Notifies the delegate, on the thread where this method is called, each time
-  // the object is set. By definition, the handle must be an auto-reset object.
-  // The caller must ensure that it (or any Windows system code) doesn't reset
-  // the event or else the delegate won't be called.
+  // Notifies the delegate, on the sequence where this method is called, each
+  // time the object is set. By definition, the handle must be an auto-reset
+  // object. The caller must ensure that it (or any Windows system code) doesn't
+  // reset the event or else the delegate won't be called.
   // Returns whether watching was successfully initiated.
   bool StartWatchingMultipleTimes(HANDLE object, Delegate* delegate);
 
@@ -112,8 +111,8 @@ class BASE_EXPORT ObjectWatcher {
   // The wait handle returned by RegisterWaitForSingleObject.
   HANDLE wait_object_ = nullptr;
 
-  // The task runner of the thread on which the watch was started.
-  scoped_refptr<SingleThreadTaskRunner> task_runner_;
+  // The task runner of the sequence on which the watch was started.
+  scoped_refptr<SequencedTaskRunner> task_runner_;
 
   bool run_once_ = true;