Fix crash on IP address change.

net/base/host_resolver.h

Index: net/base/host_resolver.h
diff --git a/net/base/host_resolver.h b/net/base/host_resolver.h
index 9fd8dbe427e9a75c5f622c1c77b2ed3f9884b51f..e4bf8476121e207b8a30b3bc8655a8cc85c9ea4a 100644
--- a/net/base/host_resolver.h
+++ b/net/base/host_resolver.h
@@ -167,9 +167,6 @@ class HostResolver : public base::RefCountedThreadSafe<HostResolver> {
   // Unregisters an observer previously added by AddObserver().
   virtual void RemoveObserver(Observer* observer) = 0;
 
-  // Gives the HostResolver an opportunity to flush state.
-  virtual void Flush() {}
-
   // Sets the default AddressFamily to use when requests have left it
   // unspecified. For example, this could be used to restrict resolution
   // results to AF_INET by passing in ADDRESS_FAMILY_IPV4, or to