Add explicit TimeDelta constexpr copy constructor.

base/time/time_win_unittest.cc

Index: base/time/time_win_unittest.cc
diff --git a/base/time/time_win_unittest.cc b/base/time/time_win_unittest.cc
index ad5e0beb40adfe7c258fc0eb3578c69bb478963a..17c722300d681d67d0010503bace12773b236585 100644
--- a/base/time/time_win_unittest.cc
+++ b/base/time/time_win_unittest.cc
@@ -19,6 +19,11 @@
 namespace base {
 namespace {
 
+// For TimeDelta::ConstexprInitialization
+constexpr int kExpectedDeltaInMilliseconds = 10;
+constexpr TimeDelta kConstexprTimeDelta =
+    TimeDelta::FromMilliseconds(kExpectedDeltaInMilliseconds);
+
 class MockTimeTicks : public TimeTicks {
  public:
   static DWORD Ticker() {
@@ -290,4 +295,9 @@ TEST(TimeTicks, FromQPCValue) {
   }
 }
 
+TEST(TimeDelta, ConstexprInitialization) {
+  // Make sure that TimeDelta works around crbug.com/635974
+  EXPECT_EQ(kExpectedDeltaInMilliseconds, kConstexprTimeDelta.InMilliseconds());

[Jeffrey Yasskin, 2016/08/12 23:07:44]

You're testing a bug in constexpr variables, so you shouldn't really use
constexpr variables on both sides of the EXPECT_EQ: the bug could cancel itself
out.

I think that's unlikely in this case because of the nature of the bug, but it'd
be a better test with a literal '10' there.

+}
+
 }  // namespace base