Add a UniqueVector class to GN

base/BUILD.gn

Index: base/BUILD.gn
diff --git a/base/BUILD.gn b/base/BUILD.gn
index 9c3ef5b8516cbb04ecaeaff86caead08d2722f7d..c0f8387bb402a8c12acd445aac2a8cf2c1fe5bb2 100644
--- a/base/BUILD.gn
+++ b/base/BUILD.gn
@@ -826,6 +826,7 @@ component("base") {
   # Windows.
   if (is_win) {
     sources -= [
+      "event_recorder_stubs.cc",
       "message_loop/message_pump_libevent.cc",
       "strings/string16.cc",
       # Not using sha1_win.cc because it may have caused a
@@ -833,6 +834,9 @@ component("base") {
       "sha1_win.cc",
     ]
 
+    # TODO(jschuh): crbug.com/167187 fix size_t to int truncations.
+    #cflags = [ "/wd4267" ]
+
     libs = [
       "netapi32.lib",
       "powrprof.lib",