Add explicit TimeDelta constexpr copy constructor.

base/time/time.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Time represents an absolute point in coordinated universal time (UTC),
 // internally represented as microseconds (s/1,000,000) since the Windows epoch
 // (1601-01-01 00:00:00 UTC). System-dependent clock interface routines are
 // defined in time_PLATFORM.cc. Note that values for Time may skew and jump
 // around as the operating system makes adjustments to synchronize (e.g., with
 // NTP servers). Thus, client code that uses the Time class must account for
@@ skipping 224 matching lines @@
   constexpr bool operator<=(TimeDelta other) const {
     return delta_ <= other.delta_;
   }
   constexpr bool operator>(TimeDelta other) const {
     return delta_ > other.delta_;
   }
   constexpr bool operator>=(TimeDelta other) const {
     return delta_ >= other.delta_;
   }
 
+#if defined(OS_WIN)
+  // This works around crbug.com/635974
+  constexpr TimeDelta(const TimeDelta& other) : delta_(other.delta_) {}
+#endif
+
  private:
   friend int64_t time_internal::SaturatedAdd(TimeDelta delta, int64_t value);
   friend int64_t time_internal::SaturatedSub(TimeDelta delta, int64_t value);
 
   // Constructs a delta given the duration in microseconds. This is private
   // to avoid confusion by callers with an integer constructor. Use
   // FromSeconds, FromMilliseconds, etc. instead.
   constexpr explicit TimeDelta(int64_t delta_us) : delta_(delta_us) {}
 
   // Private method to build a delta from a double.
@@ skipping 575 matching lines @@
   static void WaitUntilInitializedWin();
 #endif
 };
 
 // For logging use only.
 BASE_EXPORT std::ostream& operator<<(std::ostream& os, ThreadTicks time_ticks);
 
 }  // namespace base
 
 #endif  // BASE_TIME_TIME_H_