Update ClearKey to support CDM_6

media/base/cdm_promise.cc

Index: media/base/cdm_promise.cc
diff --git a/media/base/cdm_promise.cc b/media/base/cdm_promise.cc
index e57d4f49f0780f4fc80a57279d0f195c496f3134..13ee760ad6caff189c8b38e50d5d74d3babe1c1c 100644
--- a/media/base/cdm_promise.cc
+++ b/media/base/cdm_promise.cc
@@ -81,6 +81,10 @@ CdmPromiseTemplate<T>::CdmPromiseTemplate(
 }
 
 template <typename T>
+CdmPromiseTemplate<T>::CdmPromiseTemplate() {
+}
+
+template <typename T>
 CdmPromiseTemplate<T>::~CdmPromiseTemplate() {
   DCHECK(!is_pending_);
 }
@@ -131,5 +135,6 @@ void CdmPromiseTemplate<void>::resolve() {
 
 // Explicit template instantiation for the Promises needed.
 template class MEDIA_EXPORT CdmPromiseTemplate<std::string>;
+template class MEDIA_EXPORT CdmPromiseTemplate<KeyIdsVector>;
 
 }  // namespace media