Add Property to Access System ID

Adds a new property to the CDM's QueryStatus called QUERY_KEY_SYSTEM_ID that
contains the System ID. (as read from OEMCrypto_GetKeyData)  Adds a new
property to the DrmPlugin (cleverly named "systemId") that allows the app to
query for this.  Also adds unit tests.

Also changes the Device ID getter in crypto_engine.cpp to return a failure
instead of an empty ID.

Bug: 8621632

Merge of https://widevine-internal-review.googlesource.com/#/c/5010/ from
widevine cdm repository to android repository.

Change-Id: I8f309af18487c499e8ce25e829059e45623ea4dc

libwvdrmengine/cdm/core/include/crypto_engine.h

@@ -5,6 +5,7 @@
 #ifndef CDM_BASE_CRYPTO_ENGINE_H_
 #define CDM_BASE_CRYPTO_ENGINE_H_
 
+#include <stdint.h>
 #include <string>
 
 #include "crypto_session.h"
@@ -48,7 +49,8 @@ class CryptoEngine {
   } SecurityLevel;
 
   SecurityLevel GetSecurityLevel();
-  std::string GetDeviceUniqueId();
+  bool GetDeviceUniqueId(std::string* deviceId);
+  bool GetSystemId(uint32_t* systemId);
 
 private: