Add decrypt-only external clear key browser tests.

media/cdm/ppapi/clear_key_cdm.h

Index: media/cdm/ppapi/clear_key_cdm.h
diff --git a/media/cdm/ppapi/clear_key_cdm.h b/media/cdm/ppapi/clear_key_cdm.h
index c8d0703227ade000856cf530fa61b3ac246c717c..6ef4e047f26bf992ac726dc49f3a8a4c9f7ec6f4 100644
--- a/media/cdm/ppapi/clear_key_cdm.h
+++ b/media/cdm/ppapi/clear_key_cdm.h
@@ -30,7 +30,7 @@ class FFmpegCdmAudioDecoder;
 // Clear key implementation of the cdm::ContentDecryptionModule interface.
 class ClearKeyCdm : public ClearKeyCdmInterface {
  public:
-  explicit ClearKeyCdm(Host* host);
+  explicit ClearKeyCdm(Host* host, bool is_decrypt_only);
   virtual ~ClearKeyCdm();
 
   // ContentDecryptionModule implementation.
@@ -150,6 +150,8 @@ class ClearKeyCdm : public ClearKeyCdmInterface {
 
   ClearKeyCdmHost* host_;
 
+  const bool is_decrypt_only_;
+
   std::string heartbeat_session_id_;
   std::string next_heartbeat_message_;