Move ProxyResolver to common.

HttpFetcher depends on it and HttpFetcher is in common.

Bug: 28171891
Test: mma
Change-Id: I1783821c4a7d6785ee23df1cde648a3e1ea8fadf
diff --git a/update_attempter.h b/update_attempter.h
index 108a6c6..99bde83 100644
--- a/update_attempter.h
+++ b/update_attempter.h
@@ -36,11 +36,11 @@
 #include "update_engine/client_library/include/update_engine/update_status.h"
 #include "update_engine/common/action_processor.h"
 #include "update_engine/common/cpu_limiter.h"
+#include "update_engine/common/proxy_resolver.h"
 #include "update_engine/omaha_request_params.h"
 #include "update_engine/omaha_response_handler_action.h"
 #include "update_engine/payload_consumer/download_action.h"
 #include "update_engine/payload_consumer/postinstall_runner_action.h"
-#include "update_engine/proxy_resolver.h"
 #include "update_engine/service_observer_interface.h"
 #include "update_engine/system_state.h"
 #include "update_engine/update_manager/policy.h"