Report key status change

Also modified PolicyEngine::CanDecrypt to use the new Keys_status_.

Bug: 19771431

Merged from Widevine CDM repo:
https://widevine-internal-review.googlesource.com/#/c/13904/

Change-Id: If7fb7fa45ecf9ff4e65278cda00ad7230b57f50b

libwvdrmengine/mediadrm/include/WVDrmPlugin.h

@@ -32,6 +32,7 @@ using android::status_t;
 using android::String8;
 using android::Vector;
 using std::map;
+using wvcdm::CdmKeyInformation;
 using wvcdm::CdmSessionId;
 using wvcdm::CdmResponseType;
 using wvcdm::WvContentDecryptionModule;
@@ -143,6 +144,11 @@ class WVDrmPlugin : public android::DrmPlugin,
 
   virtual void OnSessionExpiration(const CdmSessionId& cdmSessionId);
 
+  virtual void OnSessionKeysChange(
+      const CdmSessionId& session_id,
+      const std::vector<CdmKeyInformation>& cdm_keys_info,
+      bool has_new_usable_key);
+
   virtual void OnExpirationUpdate(const CdmSessionId& cdmSessionId,
                                   int64_t new_expiry_time);