Have system clocks return wall time

[ Merge of http://go/wvgerrit/120445 ]

Switch TestHost and FakeClock to use chrono::system_clock (wall time)
rather than chrono::steady_clock (ticks since boot time).

Bug: 183160800
Test: CE CDM tests
Change-Id: I6ef4c02c01ff96453847ee8f42e6037c298866b5

libwvdrmengine/cdm/util/test/test_clock.cpp

@@ -17,7 +17,7 @@ namespace {
 class FakeClock : public wvcdm::TestSleep::CallBack {
  public:
   FakeClock() {
-    auto now = std::chrono::steady_clock().now();
+    auto now = std::chrono::system_clock().now();
     now_ = now.time_since_epoch() / std::chrono::milliseconds(1);
     TestSleep::set_callback(this);
   }