Improve performance of proxy resolver by tracing DNS dependencies.

net/proxy/proxy_service.cc

Index: net/proxy/proxy_service.cc
diff --git a/net/proxy/proxy_service.cc b/net/proxy/proxy_service.cc
index 17e46ed1d318e18e52c09c86155b9b1b10bca628..4866b32fb0761658e220e6440c8aadec25bec964 100644
--- a/net/proxy/proxy_service.cc
+++ b/net/proxy/proxy_service.cc
@@ -28,7 +28,6 @@
 #include "net/proxy/proxy_resolver.h"
 #include "net/proxy/proxy_script_decider.h"
 #include "net/proxy/proxy_script_fetcher.h"
-#include "net/proxy/sync_host_resolver_bridge.h"
 #include "net/url_request/url_request_context.h"
 
 #if defined(OS_WIN)
@@ -195,12 +194,6 @@ class ProxyResolverNull : public ProxyResolver {
     return LOAD_STATE_IDLE;
   }
 
-  virtual LoadState GetLoadStateThreadSafe(
-      RequestHandle request) const OVERRIDE {
-    NOTREACHED();
-    return LOAD_STATE_IDLE;
-  }
-
   virtual void CancelSetPacScript() OVERRIDE {
     NOTREACHED();
   }
@@ -238,12 +231,6 @@ class ProxyResolverFromPacString : public ProxyResolver {
     return LOAD_STATE_IDLE;
   }
 
-  virtual LoadState GetLoadStateThreadSafe(
-      RequestHandle request) const OVERRIDE {
-    NOTREACHED();
-    return LOAD_STATE_IDLE;
-  }
-
   virtual void CancelSetPacScript() OVERRIDE {
     NOTREACHED();
   }