Fix generated file dependencies for upcoming gn

services/python/content_handler/BUILD.gn

Index: services/python/content_handler/BUILD.gn
diff --git a/services/python/content_handler/BUILD.gn b/services/python/content_handler/BUILD.gn
index b4ed9877827243445d7b922a4107082bc3b76fd1..ce7059e20c545b567aefd3a2f381b21211437e0e 100644
--- a/services/python/content_handler/BUILD.gn
+++ b/services/python/content_handler/BUILD.gn
@@ -37,7 +37,10 @@ python_binary_source_set("content_handler_src") {
 }
 
 copy("common_system_pxd") {
-  visibility = [ ":mojo_system_impl" ]
+  visibility = [
+    ":mojo_system_impl",
+    ":mojo_system_impl_cython_compiler",
+  ]
   sources = [
     "//mojo/public/python/c_async_waiter.pxd",
     "//mojo/public/python/c_export.pxd",
@@ -59,7 +62,6 @@ python_binary_source_set("mojo_system_impl") {
     "python_system_impl_helper.h",
   ]
   deps = [
-    ":common_system_pxd",
     "//base",
     "//mojo/environment:chromium",
     "//mojo/common",
@@ -69,4 +71,7 @@ python_binary_source_set("mojo_system_impl") {
     "//mojo/public/cpp/bindings:callback",
     "//mojo/public/python:python_common",
   ]
+  public_deps = [
+    ":common_system_pxd",
+  ]
 }