Store key set ID with usage info

[ Merge of http://go/wvgerrit/16241 and http://go/wvgerrit/16364 ]

This will allow a usage session to be loaded later by key set ID.
This is needed for EME-style secure stop in the new CE CDM API.

b/25816911

Change-Id: I916340047492fbc0556d0e90bd2eac0f3eafe597

libwvdrmengine/cdm/core/include/cdm_engine.h

@@ -146,6 +146,8 @@ class CdmEngine {
   virtual CdmResponseType ReleaseAllUsageInfo(const std::string& app_id);
   virtual CdmResponseType ReleaseUsageInfo(
       const CdmUsageInfoReleaseMessage& message);
+  virtual CdmResponseType LoadUsageSession(const CdmKeySetId& key_set_id,
+                                           CdmKeyMessage* release_message);
 
   // Decryption and key related methods
   // Accept encrypted buffer and return decrypted data.