Remove unused HostResolver::Observer.

net/base/mock_host_resolver.h

Index: net/base/mock_host_resolver.h
diff --git a/net/base/mock_host_resolver.h b/net/base/mock_host_resolver.h
index 3c6f178220ae118ebced4da3fbc8720f7d62f530..8abc4e2efbcac27c356eb5998e5ef389f5f33196 100644
--- a/net/base/mock_host_resolver.h
+++ b/net/base/mock_host_resolver.h
@@ -10,7 +10,6 @@
 #include <map>
 
 #include "base/memory/weak_ptr.h"
-#include "base/observer_list.h"
 #include "base/synchronization/waitable_event.h"
 #include "base/threading/non_thread_safe.h"
 #include "net/base/host_resolver.h"
@@ -76,8 +75,6 @@ class MockHostResolverBase : public HostResolver,
                                AddressList* addresses,
                                const BoundNetLog& net_log) OVERRIDE;
   virtual void CancelRequest(RequestHandle req) OVERRIDE;
-  virtual void AddObserver(Observer* observer) OVERRIDE;
-  virtual void RemoveObserver(Observer* observer) OVERRIDE;
   virtual HostCache* GetHostCache() OVERRIDE;
 
  protected:
@@ -97,7 +94,6 @@ class MockHostResolverBase : public HostResolver,
   void ResolveNow(size_t id);
 
   bool synchronous_mode_;
-  ObserverList<Observer> observers_;
   scoped_refptr<RuleBasedHostResolverProc> rules_;
   scoped_refptr<HostResolverProc> proc_;
   scoped_ptr<HostCache> cache_;
@@ -193,8 +189,6 @@ class HangingHostResolver : public HostResolver {
                                AddressList* addresses,
                                const BoundNetLog& net_log) OVERRIDE;
   virtual void CancelRequest(RequestHandle req) OVERRIDE {}
-  virtual void AddObserver(Observer* observer) OVERRIDE {}
-  virtual void RemoveObserver(Observer* observer) OVERRIDE {}
 };
 
 // This class sets the default HostResolverProc for a particular scope.  The