Add support for link repros and use it on net_perftests.

net/BUILD.gn

Index: net/BUILD.gn
diff --git a/net/BUILD.gn b/net/BUILD.gn
index edacd2fc245713c3039fd2aeedd785515f795690..e71b431f06ea6e20a6c8bfa54b993395d4ad59e2 100644
--- a/net/BUILD.gn
+++ b/net/BUILD.gn
@@ -1596,6 +1596,13 @@ if (!is_ios) {
     } else {
       sources -= [ "proxy/proxy_resolver_perftest.cc" ]
     }
+
+    # Some linker failures have been observed for this target on the Win64
+    # continuous builder, see crbug.com/659369.
+    # TODO(sebmarchand): Remove this once we have some data.
+    if (is_win && linkrepro_root_dir != "") {
+      ldflags = [ "/LINKREPRO:" + linkrepro_root_dir + "/" + target_name ]
+    }
   }
 }