Use the std::chrono to get the time.

[ Merge of http://go/wvgerrit/67985 ]

Now that we can use C++11, we should use the cross-platform types for
clocks instead of the platform-specific versions.

Test: WV unit/integration tests.
Change-Id: I50318e3d1caf9e814f33f497f83c19c9f3c154a1

libwvdrmengine/oemcrypto/ref/src/oemcrypto_engine_ref.cpp

@@ -8,6 +8,7 @@
 
 #include <arpa/inet.h>
 #include <assert.h>
+#include <chrono>
 #include <string.h>
 #include <algorithm>
 #include <iostream>
@@ -90,14 +91,8 @@ SessionContext* CryptoEngine::FindSession(SessionId sid) {
 time_t CryptoEngine::OnlineTime() {
   // Use the monotonic clock for times that don't have to be stable across
   // device boots.
-  timespec current_time;
-  int gettime_result = clock_gettime(CLOCK_MONOTONIC, &current_time);
-  if (gettime_result == 0) {
-    return current_time.tv_sec;
-  } else {
-    // Can't use monotonic clock, use roll back time.
-    return RollbackCorrectedOfflineTime();
-  }
+  std::chrono::steady_clock clock;
+  return clock.now().time_since_epoch() / std::chrono::seconds(1);
 }
 
 time_t CryptoEngine::RollbackCorrectedOfflineTime() {