Implement DeviceMotionEvent API

base/observer_list_threadsafe.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef BASE_OBSERVER_LIST_THREADSAFE_H_
 #define BASE_OBSERVER_LIST_THREADSAFE_H_
 
 #include <algorithm>
 #include <map>
 
@@ skipping 138 matching lines @@
     }
     list->RemoveObserver(obs);
 
     // If RemoveObserver is called from a notification, the size will be
     // nonzero.  Instead of deleting here, the NotifyWrapper will delete
     // when it finishes iterating.
     if (list->size() == 0)
       delete context;
   }
 
+  // Returns true if the observer is in the list for the current thread.
+  // Otherwise returns false.
+  bool HasObserver(ObserverType* obs) {
+    base::PlatformThreadId thread_id = base::PlatformThread::CurrentId();
+    base::AutoLock lock(list_lock_);
+    typename ObserversListMap::iterator it = observer_lists_.find(thread_id);
+    if (it == observer_lists_.end())
+      return false;
+
+    ObserverListContext* context = it->second;
+    ObserverList<ObserverType>* list = &context->list;

[flackr, 2015/02/25 23:15:16]

nit: should be able to return context->list.HasObserver(obs) no?

[jonross, 2015/03/02 15:18:10]

Done.

+
+    return list->HasObserver(obs);
+  }
+
   // Verifies that the list is currently empty (i.e. there are no observers).
   void AssertEmpty() const {
     base::AutoLock lock(list_lock_);
     DCHECK(observer_lists_.empty());
   }
 
   // Notify methods.
   // Make a thread-safe callback to each Observer in the list.
   // Note, these calls are effectively asynchronous.  You cannot assume
   // that at the completion of the Notify call that all Observers have
@@ skipping 88 matching lines @@
       ObserversListMap;
 
   mutable base::Lock list_lock_;  // Protects the observer_lists_.
   ObserversListMap observer_lists_;
   const NotificationType type_;
 
   DISALLOW_COPY_AND_ASSIGN(ObserverListThreadSafe);
 };
 
 #endif  // BASE_OBSERVER_LIST_THREADSAFE_H_