commit db5f2b6e74d6d2e2a9c6f530199067c1d6eff7b6
Author: Max Morin <maxmorin@chromium.org>
Date:   Mon Aug 27 09:45:24 2018 +0000

    Make TimeDelta TriviallyCopyable for std::atomic.
    
    We're having some awkwardness with working around the issue with stuff
    like std::atomic<int64_t> and conversions back and forth. It would be
    preferable to use std::atomic<TimeDelta> directly.
    
    Removes the workaround added for bug 635974, since that was a bug in
    vs 2015 and we use clang now.
    
    Also fixes a couple of lint issues in time.h.
    
    Bug: 635974, 851959, 761570
    Change-Id: I4683f960b0c348748c5f0aaf222da4dda40256ec
    Reviewed-on: https://chromium-review.googlesource.com/1184781
    Commit-Queue: Max Morin <maxmorin@chromium.org>
    Reviewed-by: Yuri Wiitala <miu@chromium.org>
    Reviewed-by: Bruce Dawson <brucedawson@chromium.org>
    Cr-Commit-Position: refs/heads/master@{#586219}

diff --git a/base/time/time.h b/base/time/time.h
index f4c2f93f30b4..7d4f308545c9 100644
--- a/base/time/time.h
+++ b/base/time/time.h
@@ -199,11 +199,6 @@ class BASE_EXPORT TimeDelta {
   double InMicrosecondsF() const;
   int64_t InNanoseconds() const;
 
-  constexpr TimeDelta& operator=(TimeDelta other) {
-    delta_ = other.delta_;
-    return *this;
-  }
-
   // Computations with other deltas. Can easily be made constexpr with C++17 but
   // hard to do until then per limitations around
   // __builtin_(add|sub)_overflow in safe_math_clang_gcc_impl.h :
@@ -283,11 +278,6 @@ class BASE_EXPORT TimeDelta {
     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);
@@ -375,7 +365,7 @@ class TimeBase {
   //
   // DEPRECATED - Do not use in new code. For serializing Time values, prefer
   // Time::ToDeltaSinceWindowsEpoch().InMicroseconds(). http://crbug.com/634507
-  int64_t ToInternalValue() const { return us_; }
+  constexpr int64_t ToInternalValue() const { return us_; }
 
   // The amount of time since the origin (or "zero") point. This is a syntactic
   // convenience to aid in code readability, mainly for debugging/testing use
@@ -799,7 +789,7 @@ constexpr TimeDelta TimeDelta::FromDouble(double value) {
 // static
 constexpr TimeDelta TimeDelta::FromProduct(int64_t value,
                                            int64_t positive_value) {
-  DCHECK(positive_value > 0);
+  DCHECK(positive_value > 0);  // NOLINT, DCHECK_GT isn't constexpr.
   return value > std::numeric_limits<int64_t>::max() / positive_value
              ? Max()
              : value < std::numeric_limits<int64_t>::min() / positive_value
@@ -903,8 +893,8 @@ class BASE_EXPORT TimeTicks : public time_internal::TimeBase<TimeTicks> {
     return TimeTicks(us);
   }
 
-#if defined(OS_WIN)
  protected:
+#if defined(OS_WIN)
   typedef DWORD (*TickFunctionType)(void);
   static TickFunctionType SetMockTickFunction(TickFunctionType ticker);
 #endif
@@ -926,8 +916,7 @@ BASE_EXPORT std::ostream& operator<<(std::ostream& os, TimeTicks time_ticks);
 // thread is running.
 class BASE_EXPORT ThreadTicks : public time_internal::TimeBase<ThreadTicks> {
  public:
-  ThreadTicks() : TimeBase(0) {
-  }
+  constexpr ThreadTicks() : TimeBase(0) {}
 
   // Returns true if ThreadTicks::Now() is supported on this system.
   static bool IsSupported() WARN_UNUSED_RESULT {
diff --git a/base/time/time_unittest.cc b/base/time/time_unittest.cc
index 5dc8888a3297..ce8cc39cbaec 100644
--- a/base/time/time_unittest.cc
+++ b/base/time/time_unittest.cc
@@ -1542,6 +1542,70 @@ TEST(TimeDelta, Overflows) {
   EXPECT_EQ(kOneSecond, (ticks_now + kOneSecond) - ticks_now);
 }
 
+constexpr TimeTicks TestTimeTicksConstexprCopyAssignment() {
+  TimeTicks a = TimeTicks::FromInternalValue(12345);
+  TimeTicks b;
+  b = a;
+  return b;
+}
+
+TEST(TimeTicks, ConstexprAndTriviallyCopiable) {
+  // "Trivially copyable" is necessary for use in std::atomic<TimeTicks>.
+  static_assert(std::is_trivially_copyable<TimeTicks>(), "");
+
+  // Copy ctor.
+  constexpr TimeTicks a = TimeTicks::FromInternalValue(12345);
+  constexpr TimeTicks b{a};
+  static_assert(a.ToInternalValue() == b.ToInternalValue(), "");
+
+  // Copy assignment.
+  static_assert(a.ToInternalValue() ==
+                    TestTimeTicksConstexprCopyAssignment().ToInternalValue(),
+                "");
+}
+
+constexpr ThreadTicks TestThreadTicksConstexprCopyAssignment() {
+  ThreadTicks a = ThreadTicks::FromInternalValue(12345);
+  ThreadTicks b;
+  b = a;
+  return b;
+}
+
+TEST(ThreadTicks, ConstexprAndTriviallyCopiable) {
+  // "Trivially copyable" is necessary for use in std::atomic<ThreadTicks>.
+  static_assert(std::is_trivially_copyable<ThreadTicks>(), "");
+
+  // Copy ctor.
+  constexpr ThreadTicks a = ThreadTicks::FromInternalValue(12345);
+  constexpr ThreadTicks b{a};
+  static_assert(a.ToInternalValue() == b.ToInternalValue(), "");
+
+  // Copy assignment.
+  static_assert(a.ToInternalValue() ==
+                    TestThreadTicksConstexprCopyAssignment().ToInternalValue(),
+                "");
+}
+
+constexpr TimeDelta TestTimeDeltaConstexprCopyAssignment() {
+  TimeDelta a = TimeDelta::FromSeconds(1);
+  TimeDelta b;
+  b = a;
+  return b;
+}
+
+TEST(TimeDelta, ConstexprAndTriviallyCopiable) {
+  // "Trivially copyable" is necessary for use in std::atomic<TimeDelta>.
+  static_assert(std::is_trivially_copyable<TimeDelta>(), "");
+
+  // Copy ctor.
+  constexpr TimeDelta a = TimeDelta::FromSeconds(1);
+  constexpr TimeDelta b{a};
+  static_assert(a == b, "");
+
+  // Copy assignment.
+  static_assert(a == TestTimeDeltaConstexprCopyAssignment(), "");
+}
+
 TEST(TimeDeltaLogging, DCheckEqCompiles) {
   DCHECK_EQ(TimeDelta(), TimeDelta());
 }