Make the Windows multi_dll build work in GN

base/trace_event/etw_manifest/BUILD.gn

 # Copyright 2015 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 assert(is_win, "This only runs on Windows.")
 
 # Makes the .h/.rc files from the .man file.
-action("chrome_events_win") {
-  visibility = [
-    "//base/trace_event/*",
-    "//chrome:main_dll",
-  ]
+action("chrome_events_win_generate") {
+  visibility = [ ":*" ]
   script = "build/message_compiler.py"
 
   sources = [
     "chrome_events_win.man",
   ]
 
   outputs = [
     "$target_gen_dir/chrome_events_win.h",
     "$target_gen_dir/chrome_events_win.rc",
   ]
 
   args = [
     # Where to put the header.
     "-h",
     rebase_path("$target_gen_dir", root_build_dir),
 
     # Where to put the .rc file.
     "-r",
     rebase_path("$target_gen_dir", root_build_dir),
 
     # Generate the user-mode code.
     "-um",
     rebase_path("chrome_events_win.man", root_build_dir),
   ]
 }
+
+# Compile the generated files.
+source_set("chrome_events_win") {
+  visibility = [
+    "//base/trace_event/*",
+    "//chrome:main_dll",
+  ]
+
+  sources = get_target_outputs(":chrome_events_win_generate")
+
+  deps = [
+    ":chrome_events_win_generate",
+  ]
+}