Implement DeviceMotionEvent API

base/observer_list_threadsafe.h

Index: base/observer_list_threadsafe.h
diff --git a/base/observer_list_threadsafe.h b/base/observer_list_threadsafe.h
index 1a6633372b8da5ac8589eef0f4dfe79f2ebaef7b..c0e18facbbf83e7b8fb0d936490b26632952512f 100644
--- a/base/observer_list_threadsafe.h
+++ b/base/observer_list_threadsafe.h
@@ -156,6 +156,19 @@ class ObserverListThreadSafe
       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;
+    return context->list.HasObserver(obs);
+  }
+
   // Verifies that the list is currently empty (i.e. there are no observers).
   void AssertEmpty() const {
     base::AutoLock lock(list_lock_);