Add an explicit ObjectWatcher::IsWatching() method

This removes the need to compare a raw handle against
a predefined value from the caller's code.

BUG=none
TEST=base_unittests

Review URL: https://codereview.chromium.org/868143004

Cr-Commit-Position: refs/heads/master@{#314687}

base/win/object_watcher.cc

@@ -77,7 +77,11 @@ bool ObjectWatcher::StopWatching() {
   return true;
 }
 
-HANDLE ObjectWatcher::GetWatchedObject() {
+bool ObjectWatcher::IsWatching() const {
+  return object_ != NULL;
+}
+
+HANDLE ObjectWatcher::GetWatchedObject() const {
   return object_;
 }
 

base/win/object_watcher.h

@@ -74,9 +74,11 @@ class BASE_EXPORT ObjectWatcher : public MessageLoop::DestructionObserver {
   //
   bool StopWatching();
 
-  // Returns the handle of the object being watched, or NULL if the object
-  // watcher is stopped.
-  HANDLE GetWatchedObject();
+  // Returns true if currently watching an object.
+  bool IsWatching() const;
+
+  // Returns the handle of the object being watched.
+  HANDLE GetWatchedObject() const;
 
  private:
   // Called on a background thread when done waiting.

base/win/object_watcher_unittest.cc

@@ -37,7 +37,7 @@ void RunTest_BasicSignal(MessageLoop::Type message_loop_type) {
   MessageLoop message_loop(message_loop_type);
 
   ObjectWatcher watcher;
-  EXPECT_EQ(NULL, watcher.GetWatchedObject());
+  EXPECT_FALSE(watcher.IsWatching());
 
   // A manual-reset event that is not yet signaled.
   HANDLE event = CreateEvent(NULL, TRUE, FALSE, NULL);
@@ -45,13 +45,14 @@ void RunTest_BasicSignal(MessageLoop::Type message_loop_type) {
   QuitDelegate delegate;
   bool ok = watcher.StartWatching(event, &delegate);
   EXPECT_TRUE(ok);
+  EXPECT_TRUE(watcher.IsWatching());
   EXPECT_EQ(event, watcher.GetWatchedObject());
 
   SetEvent(event);
 
   MessageLoop::current()->Run();
 
-  EXPECT_EQ(NULL, watcher.GetWatchedObject());
+  EXPECT_FALSE(watcher.IsWatching());
   CloseHandle(event);
 }
 
@@ -115,7 +116,7 @@ void RunTest_SignalBeforeWatch(MessageLoop::Type message_loop_type) {
 
   MessageLoop::current()->Run();
 
-  EXPECT_EQ(NULL, watcher.GetWatchedObject());
+  EXPECT_FALSE(watcher.IsWatching());
   CloseHandle(event);
 }