Add Go build support for GN.

mojo/go/system/embedder/embedder.go

Index: mojo/go/system/embedder/embedder.go
diff --git a/media/base/browser_cdm.cc b/mojo/go/system/embedder/embedder.go
similarity index 55%
copy from media/base/browser_cdm.cc
copy to mojo/go/system/embedder/embedder.go
index 2c44e1652ad09cf59125a471c051a86609347325..6f605dfd5e0f4b0176a6dc91e3ec6a343dda31ad 100644
--- a/media/base/browser_cdm.cc
+++ b/mojo/go/system/embedder/embedder.go
@@ -2,14 +2,13 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#include "media/base/browser_cdm.h"
+package embedder;
 
-namespace media {
+/*
+#include "mojo/go/c_embedder/c_embedder.h"
+*/
+import "C"
 
-BrowserCdm::BrowserCdm() {
+func InitializeMojoEmbedder() {
+	C.InitializeMojoEmbedder();
 }
-
-BrowserCdm::~BrowserCdm() {
-}
-
-}  // namespace media