Clock consistency checks

[ Merge from http://go/wvgerrit/33440 ]

Introduce checks to guard against clock tampering.

Bug: 62037413

Test: WV unit, integration tests on angler
Test: Manual clock rollback test
Test: Playback testing (Netflix, Play movies) on sailfish
Test: GTS test on angler
Change-Id: I47938109adb5c0f5e9aefc58eb5dac156b9f16ef

libwvdrmengine/cdm/core/include/policy_engine.h

@@ -160,6 +160,9 @@ class PolicyEngine {
   // expiry time changes.
   void NotifyExpirationUpdate(int64_t current_time);
 
+  // Guard against clock rollbacks
+  int64_t GetCurrentTime();
+
   // set_clock() is for testing only. It alters ownership of the
   // passed-in pointer.
   void set_clock(Clock* clock);
@@ -191,6 +194,9 @@ class PolicyEngine {
   // calculate the time where renewal retries should occur.
   int64_t next_renewal_time_;
 
+  // to assist in clock rollback checks
+  int64_t last_recorded_current_time_;
+
   // Used to dispatch CDM events.
   CdmSessionId session_id_;
   WvCdmEventListener* event_listener_;