Revert of Revert of Adding CopresenceState

components/copresence/public/copresence_observer.h

Index: components/copresence/public/copresence_observer.h
diff --git a/components/copresence/public/copresence_observer.h b/components/copresence/public/copresence_observer.h
new file mode 100644
index 0000000000000000000000000000000000000000..1e28726927e53815f46a38f2af352171927db6cc
--- /dev/null
+++ b/components/copresence/public/copresence_observer.h
@@ -0,0 +1,35 @@
+// Copyright 2014 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 COMPONENTS_COPRESENCE_PUBLIC_COPRESENCE_OBSERVER_H_
+#define COMPONENTS_COPRESENCE_PUBLIC_COPRESENCE_OBSERVER_H_
+
+namespace copresence {
+
+class Directive;
+struct TransmittedToken;
+struct ReceivedToken;
+
+// Implement this interface to be notified of changes
+// to the state of the copresence component.
+// TODO(ckehoe): Create a LoggingObserver based on this that replaces
+// equivalent logging elsewhere. Then we know what state is being recorded.
+class CopresenceObserver {
+ public:
+  // Called when the list of active directives has changed.
+  virtual void DirectivesUpdated() = 0;
+
+  // Called when a token is transmitted.
+  virtual void TokenTransmitted(const TransmittedToken& token) = 0;
+
+  // Called when a token is received.
+  virtual void TokenReceived(const ReceivedToken& token) = 0;
+
+ protected:
+  virtual ~CopresenceObserver() {}
+};
+
+}  // namespace copresence
+
+#endif  // COMPONENTS_COPRESENCE_PUBLIC_COPRESENCE_OBSERVER_H_