Factor out NetworkID and caching mechanism from n_q_e.{h,cc}

net/nqe/network_quality.cc

Index: net/nqe/network_quality.cc
diff --git a/net/nqe/network_quality.cc b/net/nqe/network_quality.cc
index 94bcc80357d6efaa21e77cecb44b9a90ced042fc..0e5338569b278878268eec92ec7c308256da93bd 100644
--- a/net/nqe/network_quality.cc
+++ b/net/nqe/network_quality.cc
@@ -40,6 +40,12 @@ NetworkQuality& NetworkQuality::operator=(const NetworkQuality& other) {
   return *this;
 }
 
+bool NetworkQuality::operator==(const NetworkQuality& other) const {
+  return http_rtt_ == other.http_rtt_ &&
+         transport_rtt_ == other.transport_rtt_ &&
+         downstream_throughput_kbps_ == other.downstream_throughput_kbps_;
+}
+
 }  // namespace internal
 
 }  // namespace nqe