Implement exponential backoff for failed Me2Me authentication attempts

remoting/host/chromoting_host.h

Index: remoting/host/chromoting_host.h
diff --git a/remoting/host/chromoting_host.h b/remoting/host/chromoting_host.h
index 20e7e6d0f63560b2c6cc30a00017b0574ca7f5fb..28a613d850226323d4e500ebd0b2ebd4943cc46e 100644
--- a/remoting/host/chromoting_host.h
+++ b/remoting/host/chromoting_host.h
@@ -11,6 +11,7 @@
 #include "base/memory/scoped_ptr.h"
 #include "base/observer_list.h"
 #include "base/threading/thread.h"
+#include "net/base/backoff_entry.h"
 #include "remoting/base/encoder.h"
 #include "remoting/host/capturer.h"
 #include "remoting/host/client_session.h"
@@ -203,6 +204,9 @@ class ChromotingHost : public base::RefCountedThreadSafe<ChromotingHost>,
   // Configuration of the protocol.
   scoped_ptr<protocol::CandidateSessionConfig> protocol_config_;
 
+  // Login backoff state.
+  net::BackoffEntry login_backoff_;
+
   // Flags used for RejectAuthenticatingClient().
   bool authenticating_client_;
   bool reject_authenticating_client_;