Disable static pins in TLS13DowngradeMetricsTest.

The tests need to test mail.google.com with known and unknown roots, to
check that some of the metrics work correctly. This trips the pin list
on Chrome builders. Disable the pins to avoid this.

Bug: 895801
Change-Id: Iee41b9729157bb71df0ba5619ce83e9bef5255eb
Reviewed-on: https://chromium-review.googlesource.com/c/1283933Reviewed-by: Steven Valdez <svaldez@chromium.org>
Commit-Queue: David Benjamin <davidben@chromium.org>
Cr-Commit-Position: refs/heads/master@{#600079}

net/socket/ssl_client_socket_unittest.cc

@@ -4945,9 +4945,25 @@ const TLS13DowngradeMetricsParams kTLS13DowngradeMetricsParams[] = {
      3},
 };
 
+namespace {
+namespace test_default {
+#include "net/http/transport_security_state_static_unittest_default.h"
+}  // namespace test_default
+}  // namespace
+
 class TLS13DowngradeMetricsTest
     : public SSLClientSocketTest,
-      public ::testing::WithParamInterface<TLS13DowngradeMetricsParams> {};
+      public ::testing::WithParamInterface<TLS13DowngradeMetricsParams> {
+ public:
+  TLS13DowngradeMetricsTest() {
+    // Switch the static preload list, so the tests using mail.google.com below
+    // do not trip the usual pins.
+    SetTransportSecurityStateSourceForTesting(&test_default::kHSTSSource);
+  }
+  ~TLS13DowngradeMetricsTest() {
+    SetTransportSecurityStateSourceForTesting(nullptr);
+  }
+};
 
 INSTANTIATE_TEST_CASE_P(/* no prefix */,
                         TLS13DowngradeMetricsTest,