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/cdm_session.h

@@ -265,6 +265,8 @@ class CdmSession {
 
   bool HasRootOfTrustBeenRenewed();
 
+  CdmResponseType ResetCryptoSession();
+
   // These setters are for testing only. Takes ownership of the pointers.
   void set_license_parser(CdmLicense* license_parser);
   void set_crypto_session(CryptoSession* crypto_session);
@@ -340,8 +342,9 @@ class CdmSession {
   bool has_license_been_loaded_ = false;
   bool has_license_been_restored_ = false;
 
-  bool mock_license_parser_in_use_;
-  bool mock_policy_engine_in_use_;
+  bool mock_crypto_session_in_use_ = false;
+  bool mock_license_parser_in_use_ = false;
+  bool mock_policy_engine_in_use_ = false;
 
   CORE_DISALLOW_COPY_AND_ASSIGN(CdmSession);
 };