QUIC - add new UMA histograms to help understand HPACK head of line blocking.

net/quic/quic_chromium_client_session.cc

Index: net/quic/quic_chromium_client_session.cc
diff --git a/net/quic/quic_chromium_client_session.cc b/net/quic/quic_chromium_client_session.cc
index 91f763c9d6dcdf6b4186589fe9adbb173342e40d..404f2428280200fe7039dcb2c6360562b146d970 100644
--- a/net/quic/quic_chromium_client_session.cc
+++ b/net/quic/quic_chromium_client_session.cc
@@ -185,6 +185,20 @@ void QuicChromiumClientSession::StreamRequest::OnRequestCompleteFailure(
   base::ResetAndReturn(&callback_).Run(rv);
 }
 
+void QuicChromiumClientSession::HpackEncoderDebugVisitor::OnUseEntry(
+    const QuicTime::Delta elapsed) {
+  UMA_HISTOGRAM_TIMES(
+      "Net.QuicHpackEncoderIndexedEntryAge",
+      base::TimeDelta::FromMicroseconds(elapsed.ToMicroseconds()));
+}
+
+void QuicChromiumClientSession::HpackDecoderDebugVisitor::OnUseEntry(
+    const QuicTime::Delta elapsed) {
+  UMA_HISTOGRAM_TIMES(
+      "Net.QuicHpackDecoderIndexedEntryAge",
+      base::TimeDelta::FromMicroseconds(elapsed.ToMicroseconds()));
+}
+
 QuicChromiumClientSession::QuicChromiumClientSession(
     QuicConnection* connection,
     std::unique_ptr<DatagramClientSocket> socket,
@@ -368,6 +382,16 @@ QuicChromiumClientSession::~QuicChromiumClientSession() {
       static_cast<base::HistogramBase::Sample>(stats.max_sequence_reordering));
 }
 
+void QuicChromiumClientSession::Initialize() {
+  QuicClientSessionBase::Initialize();
+  headers_stream()->SetHpackEncoderDebugVisitor(
+      std::unique_ptr<HpackEncoderDebugVisitor>(

[Ryan Hamilton, 2016/05/20 21:27:18]

fwiw, you can use base::WrapUnique(new ...) to save some verbosity.

[Buck, 2016/05/20 21:41:31]

Done.

+          new HpackEncoderDebugVisitor()));
+  headers_stream()->SetHpackDecoderDebugVisitor(
+      std::unique_ptr<HpackDecoderDebugVisitor>(
+          new HpackDecoderDebugVisitor()));
+}
+
 void QuicChromiumClientSession::OnHeadersHeadOfLineBlocking(
     QuicTime::Delta delta) {
   UMA_HISTOGRAM_TIMES(