Migrate browser_test_utils.cc to use net::GzipSourceStream

net::GzipFilter will soon be removed. This CL migrates browser_test_utils.cc
to use net::GzipSourceStream.

BUG=474859

Review-Url: https://codereview.chromium.org/2485523003
Cr-Commit-Position: refs/heads/master@{#430613}
diff --git a/net/BUILD.gn b/net/BUILD.gn
index 23cb623..7a8233b9c 100644
--- a/net/BUILD.gn
+++ b/net/BUILD.gn
@@ -518,6 +518,8 @@
     "dns/mock_host_resolver.h",
     "dns/mock_mdns_socket_factory.cc",
     "dns/mock_mdns_socket_factory.h",
+    "filter/mock_source_stream.cc",
+    "filter/mock_source_stream.h",
     "http/http_stream_factory_test_util.cc",
     "http/http_stream_factory_test_util.h",
     "http/http_transaction_test_util.cc",