Reset crypto session pointers on RemoveKeys.

[ Merge of http://go/wvgerrit/189590 ]
[ Cherry-pick of http://ag/26541307 ]

The CDM session shares its CryptoSession instance with a few additional
member objects (CdmLicense and PolicyEngine).  When the CDM session's
crypto session is reset, it must also reset the CdmLicense and
PolicyEngine otherwise, a potential stale pointer reference may occur.

Test: request_license_test on Oriole
Test: run_x86_64_tests
Bug: 311239278
Change-Id: Ie175513ae652dcd96e12e5e1def574a8a56d5863

libwvdrmengine/cdm/core/include/license.h

@@ -90,6 +90,15 @@ class CdmLicense {
       const CdmKeyResponse& license_response,
       std::string* provider_session_token);
 
+  // Testing only.  Caller retains ownership of pointers.
+  void set_crypto_session(CryptoSession* crypto_session) {
+    crypto_session_ = crypto_session;
+  }
+
+  void set_policy_engine(PolicyEngine* policy_engine) {
+    policy_engine_ = policy_engine;
+  }
+
  private:
   CdmResponseType HandleKeyErrorResponse(
       const video_widevine::SignedMessage& signed_message);
@@ -131,8 +140,8 @@ class CdmLicense {
   bool SetTypeAndId(CdmLicenseType license_type, const std::string& request_id,
                     T* content_id);
 
-  CryptoSession* crypto_session_;
-  PolicyEngine* policy_engine_;
+  CryptoSession* crypto_session_ = nullptr;
+  PolicyEngine* policy_engine_ = nullptr;
   std::string server_url_;
   std::string client_token_;
   const CdmSessionId session_id_;