Fix base::is_trivially_copyable to detect destructors.

std::is_trivially_copyable should return false for classes with nontrivial
destructors.

C++11 standard section 9.6 says a trivially copyable class is a class that:
  — has no non-trivial copy constructors (12.8),
  — has no non-trivial move constructors (12.8),
  — has no non-trivial copy assignment operators (13.5.3, 12.8),
  — has no non-trivial move assignment operators (13.5.3, 12.8), and
  — has a trivial destructor (12.4).

The current implementation for _GNUC_VER < 501 didn't detech the destructor
case. This is important because when is_trivially_copyable returns true,
container code may implement moves as memcpy, when in fact it needs to me a
memcpy + a destructor.

Bug: 
Change-Id: I5739856ca7eaf5ddcf3eeb716bdc2dc33b0de0f2
Reviewed-on: https://chromium-review.googlesource.com/575020Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Commit-Queue: Brett Wilson <brettw@chromium.org>
Cr-Commit-Position: refs/heads/master@{#487237}

base/template_util.h

@@ -87,7 +87,8 @@ struct is_trivially_copyable {
 #if _GNUC_VER >= 501
   static constexpr bool value = __is_trivially_copyable(T);
 #else
-  static constexpr bool value = __has_trivial_copy(T);
+  static constexpr bool value =
+      __has_trivial_copy(T) && __has_trivial_destructor(T);
 #endif
 };
 #else

base/template_util_unittest.cc

@@ -69,5 +69,26 @@ static_assert(
     internal::SupportsOstreamOperator<const StructWithOperator&>::value,
     "struct with operator<< should be printable by const ref");
 
+// base::is_trivially_copyable
+class TrivialCopy {
+ public:
+  TrivialCopy(int d) : data_(d) {}
+
+ protected:
+  int data_;
+};
+
+class TrivialCopyButWithDestructor : public TrivialCopy {
+ public:
+  TrivialCopyButWithDestructor(int d) : TrivialCopy(d) {}
+  ~TrivialCopyButWithDestructor() { data_ = 0; }
+};
+
+static_assert(base::is_trivially_copyable<TrivialCopy>::value,
+              "TrivialCopy should be detected as trivially copyable");
+static_assert(!base::is_trivially_copyable<TrivialCopyButWithDestructor>::value,
+              "TrivialCopyButWithDestructor should not be detected as "
+              "trivially copyable");
+
 }  // namespace
 }  // namespace base