media: Make MediaKeys ref-counted.

media/base/media_keys.cc

Index: media/base/media_keys.cc
diff --git a/media/base/media_keys.cc b/media/base/media_keys.cc
index cf5256bf2333966ee5161dc1fd93297db51bf546..03e7acf706cf6936800a7949d361084bc064e324 100644
--- a/media/base/media_keys.cc
+++ b/media/base/media_keys.cc
@@ -10,4 +10,13 @@ MediaKeys::MediaKeys() {}
 
 MediaKeys::~MediaKeys() {}
 
+void MediaKeys::DeleteOnCorrectThread() const {
+  delete this;
+}
+
+// static
+void MediaKeysTraits::Destruct(const MediaKeys* media_keys) {
+  media_keys->DeleteOnCorrectThread();
+}
+
 }  // namespace media