Use mock proxy client socket in some tests.

This is necessary to avoid creating a DefaultClientSocketFactory, which
is a leaky singleton and therefore would hold a reference to
ScopedTaskEnvironment's reference counted MockTimeTaskRunner forever,
thus preventing the creating of another ScopedTaskEnvironment.

This is prework for https://crrev.com/c/1037405.

Bug: 791831
Change-Id: Iba9e17cc51d7002318f3a27d694b3d9230f36d4e
Reviewed-on: https://chromium-review.googlesource.com/1037324Reviewed-by: Helen Li <xunjieli@chromium.org>
Commit-Queue: Bence Béky <bnc@chromium.org>
Cr-Commit-Position: refs/heads/master@{#556028}

net/http/http_stream_factory_job_controller_unittest.cc

@@ -1865,6 +1865,10 @@ TEST_F(HttpStreamFactoryJobControllerTest, DelayedTCPAlternativeProxy) {
 // Verifies that if the alternative proxy server job fails immediately, the
 // main job is not blocked.
 TEST_F(HttpStreamFactoryJobControllerTest, FailAlternativeProxy) {
+  session_deps_.socket_factory->UseMockProxyClientSockets();
+  ProxyClientSocketDataProvider proxy_data(SYNCHRONOUS, OK);
+  session_deps_.socket_factory->AddProxyClientSocketDataProvider(&proxy_data);
+
   quic_data_ = std::make_unique<MockQuicData>();
   quic_data_->AddConnect(SYNCHRONOUS, ERR_FAILED);
   tcp_data_ = std::make_unique<SequencedSocketData>(nullptr, 0, nullptr, 0);
@@ -1914,6 +1918,10 @@ TEST_F(HttpStreamFactoryJobControllerTest, FailAlternativeProxy) {
 // disconnection, then the proxy delegate is not notified.
 TEST_F(HttpStreamFactoryJobControllerTest,
        InternetDisconnectedAlternativeProxy) {
+  session_deps_.socket_factory->UseMockProxyClientSockets();
+  ProxyClientSocketDataProvider proxy_data(SYNCHRONOUS, OK);
+  session_deps_.socket_factory->AddProxyClientSocketDataProvider(&proxy_data);
+
   quic_data_ = std::make_unique<MockQuicData>();
   quic_data_->AddConnect(SYNCHRONOUS, ERR_INTERNET_DISCONNECTED);
   tcp_data_ = std::make_unique<SequencedSocketData>(nullptr, 0, nullptr, 0);
@@ -1960,6 +1968,10 @@ TEST_F(HttpStreamFactoryJobControllerTest,
        AlternativeProxyServerJobFailsAfterMainJobSucceeds) {
   base::HistogramTester histogram_tester;
 
+  session_deps_.socket_factory->UseMockProxyClientSockets();
+  ProxyClientSocketDataProvider proxy_data(SYNCHRONOUS, OK);
+  session_deps_.socket_factory->AddProxyClientSocketDataProvider(&proxy_data);
+
   // Use COLD_START to make the alt job pending.
   crypto_client_stream_factory_.set_handshake_mode(
       MockCryptoClientStream::COLD_START);