Add QuicStrCat.

net/net.gypi

Index: net/net.gypi
diff --git a/net/net.gypi b/net/net.gypi
index c73346bb4720695d4f259f19e207ee915a4af39b..21eb7b82e16b4d8ad4d2fb487a8dcfca37588c97 100644
--- a/net/net.gypi
+++ b/net/net.gypi
@@ -1215,6 +1215,7 @@
       'quic/platform/api/quic_reference_counted.h',
       'quic/platform/api/quic_socket_address.cc',
       'quic/platform/api/quic_socket_address.h',
+      'quic/platform/api/quic_str_cat.h',
       'quic/platform/impl/quic_chromium_clock.cc',
       'quic/platform/impl/quic_chromium_clock.h',
       'quic/platform/impl/quic_ip_address_impl.cc',
@@ -1224,6 +1225,7 @@
       'quic/platform/impl/quic_reference_counted_impl.h',
       'quic/platform/impl/quic_socket_address_impl.cc',
       'quic/platform/impl/quic_socket_address_impl.h',
+      'quic/platform/impl/quic_str_cat_impl.h',
       'quic/quartc/quartc_alarm_factory.cc',
       'quic/quartc/quartc_alarm_factory.h',
       'quic/quartc/quartc_factory.cc',
@@ -1958,6 +1960,7 @@
       'quic/core/quic_write_blocked_list_test.cc',
       'quic/core/spdy_utils_test.cc',
       'quic/platform/api/quic_reference_counted_test.cc',
+      'quic/platform/api/quic_str_cat_test.cc',
       'quic/platform/impl/quic_chromium_clock_test.cc',
       'quic/quartc/quartc_alarm_factory_test.cc',
       'quic/quartc/quartc_session_test.cc',