Server push cancellation: add a finch trial parameter

net/http/http_cache.cc

Index: net/http/http_cache.cc
diff --git a/net/http/http_cache.cc b/net/http/http_cache.cc
index bf423eccf48f79822767518d49828fc0e94c11e3..93d39cc9a936f391ba6cc06ec9c20a92ac5bbe14 100644
--- a/net/http/http_cache.cc
+++ b/net/http/http_cache.cc
@@ -38,6 +38,7 @@
 #include "net/base/upload_data_stream.h"
 #include "net/disk_cache/disk_cache.h"
 #include "net/http/disk_cache_based_quic_server_info.h"
+#include "net/http/http_cache_lookup_manager.h"
 #include "net/http/http_cache_transaction.h"
 #include "net/http/http_network_layer.h"
 #include "net/http/http_network_session.h"
@@ -343,14 +344,20 @@ HttpCache::HttpCache(std::unique_ptr<HttpTransactionFactory> network_layer,
   // Session may be NULL in unittests.
   // TODO(mmenke): Seems like tests could be changed to provide a session,
   // rather than having logic only used in unit tests here.
-  if (session) {
-    net_log_ = session->net_log();
-    if (is_main_cache &&
-        !session->quic_stream_factory()->has_quic_server_info_factory()) {
-      // QuicStreamFactory takes ownership of QuicServerInfoFactoryAdaptor.
-      session->quic_stream_factory()->set_quic_server_info_factory(
-          new QuicServerInfoFactoryAdaptor(this));
-    }
+  if (!session)
+    return;
+
+  net_log_ = session->net_log();
+  if (!is_main_cache)
+    return;
+
+  session->SetServerPushDelegate(
+      base::MakeUnique<HttpCacheLookupManager>(this));
+
+  if (!session->quic_stream_factory()->has_quic_server_info_factory()) {
+    // QuicStreamFactory takes ownership of QuicServerInfoFactoryAdaptor.
+    session->quic_stream_factory()->set_quic_server_info_factory(
+        new QuicServerInfoFactoryAdaptor(this));
   }
 }