Remove unused HostResolver::Observer.

net/proxy/sync_host_resolver_bridge_unittest.cc

Index: net/proxy/sync_host_resolver_bridge_unittest.cc
diff --git a/net/proxy/sync_host_resolver_bridge_unittest.cc b/net/proxy/sync_host_resolver_bridge_unittest.cc
index 327c44d430d8a6ec77b95171561a5ca9c704050e..36586d3281de7c4688e3010452e04887f4e0b986 100644
--- a/net/proxy/sync_host_resolver_bridge_unittest.cc
+++ b/net/proxy/sync_host_resolver_bridge_unittest.cc
@@ -59,14 +59,6 @@ class BlockableHostResolver : public HostResolver {
     was_request_cancelled_ = true;
   }
 
-  virtual void AddObserver(Observer* observer) OVERRIDE {
-    NOTREACHED();
-  }
-
-  virtual void RemoveObserver(Observer* observer) OVERRIDE {
-    NOTREACHED();
-  }
-
   // Waits until Resolve() has been called.
   void WaitUntilRequestIsReceived() {
     event_.Wait();