Prevent race conditions between decrypt and close session

[ Merge of http://go/wvgerrit/47520 ]

Bug: 73781703
Test: WV unit/integration tests, GTS GtsMediaTestCases tests and AUPT tests.
Change-Id: I618ed8ca38855aecdb31e829a7f4041cbd505a02

libwvdrmengine/cdm/core/include/cdm_session.h

@@ -37,7 +37,7 @@ class CdmSession {
   CdmSession(FileSystem* file_system, metrics::SessionMetrics* metrics);
   virtual ~CdmSession();
 
-  void Close() { closed_ = true; }
+  void Close();
   bool IsClosed() { return closed_; }
 
   // Initializes this instance of CdmSession with the given property set.
@@ -263,6 +263,9 @@ class CdmSession {
   bool mock_license_parser_in_use_;
   bool mock_policy_engine_in_use_;
 
+  // Lock to avoid race conditions between Close() and Decrypt()
+  Lock close_lock_;
+
   CORE_DISALLOW_COPY_AND_ASSIGN(CdmSession);
 };