NQE: Discard RTT and throughput observations from non-GET requests

Cq-Include-Trybots: master.tryserver.chromium.android:android_cronet_tester;master.tryserver.chromium.mac:ios-simulator-cronet
Bug: 782780
Change-Id: I419786e99fa6f794d5c84041f131254588328d9f
Reviewed-on: https://chromium-review.googlesource.com/758721
Commit-Queue: Tarun Bansal <tbansal@chromium.org>
Reviewed-by: Ryan Sturm <ryansturm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#515061}

net/nqe/network_quality_estimator.cc

@@ -738,7 +738,8 @@ bool NetworkQualityEstimator::RequestProvidesRTTObservation(
          // response is not cached.
          !request.response_info().response_time.is_null() &&
          !request.was_cached() &&
-         request.creation_time() >= last_connection_change_;
+         request.creation_time() >= last_connection_change_ &&
+         request.method() == "GET";
 }
 
 void NetworkQualityEstimator::RecordExternalEstimateProviderMetrics(

net/nqe/throughput_analyzer.cc

@@ -29,6 +29,12 @@ namespace {
 // degrade accuracy held in the memory.
 static const size_t kMaxRequestsSize = 300;
 
+// Returns true if the request should be discarded because it does not provide
+// meaningful observation.
+bool ShouldDiscardRequest(const URLRequest& request) {
+  return request.method() != "GET";
+}
+
 }  // namespace
 
 namespace nqe {
@@ -136,6 +142,8 @@ void ThroughputAnalyzer::NotifyStartTransaction(const URLRequest& request) {
     EndThroughputObservationWindow();
     DCHECK(!IsCurrentlyTrackingThroughput());
     return;
+  } else if (ShouldDiscardRequest(request)) {
+    return;
   }
 
   EraseHangingRequests(request);