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_ref.cpp

@@ -15,8 +15,7 @@
 #include <stdint.h>
 #include <stdio.h>
 #include <string.h>
-#include <sys/time.h>
-#include <time.h>
+#include <chrono>
 #include <iostream>
 #include <string>
 #include <utility>
@@ -162,12 +161,6 @@ OEMCRYPTO_API OEMCryptoResult OEMCrypto_GenerateDerivedKeys(
   return OEMCrypto_SUCCESS;
 }
 
-static const uint64_t one_second = 1000000ull;
-static uint64_t TimeStamp(void) {
-  struct timeval tv;
-  gettimeofday(&tv,NULL);
-  return tv.tv_sec * one_second + tv.tv_usec;
-}
 
 OEMCRYPTO_API OEMCryptoResult OEMCrypto_GenerateNonce(OEMCrypto_SESSION session,
                                                       uint32_t* nonce) {
@@ -182,13 +175,14 @@ OEMCRYPTO_API OEMCryptoResult OEMCrypto_GenerateNonce(OEMCrypto_SESSION session,
   }
 
   // Prevent nonce flood.
-  uint64_t now = TimeStamp();
-  static uint64_t last_nonce_time = now;
+  static std::chrono::steady_clock clock;
+  const auto now = clock.now().time_since_epoch();
+  static auto last_nonce_time = now;
   // For testing, we set nonce_flood_count to 1.  Since count is initialized to
   // 1, the very first nonce after initialization is counted as a flood.
   static int nonce_count = 1;
 
-  if (now - last_nonce_time < one_second) {
+  if (now - last_nonce_time < std::chrono::seconds(1)) {
     nonce_count++;
     if (nonce_count > crypto_engine->nonce_flood_count()) {
       LOGE("[OEMCrypto_GenerateNonce(): Nonce Flood detected]");