Adding death tests to span bounds checks.

These tests should ensure that bounds are being checked for span
functions and that these guarantees don't decay.

R=palmer@chromium.org
BUG=817982

Change-Id: Ief96bcc56a78187c615cbb15e906320290eafc59
Reviewed-on: https://chromium-review.googlesource.com/c/1317894Reviewed-by: Chris Palmer <palmer@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Commit-Queue: Gabriela Melchior <gabimelchior@google.com>
Cr-Commit-Position: refs/heads/master@{#606017}

base/containers/span_unittest.cc

@@ -1183,4 +1183,18 @@ TEST(SpanTest, EnsureConstexprGoodness) {
   EXPECT_EQ(kArray[size], item);
 }
 
+TEST(SpanTest, OutOfBoundsDeath) {
+  constexpr span<int, 0> kEmptySpan;
+
+  ASSERT_DEATH_IF_SUPPORTED(kEmptySpan[0], "");
+
+  ASSERT_DEATH_IF_SUPPORTED(kEmptySpan(0), "");
+
+  ASSERT_DEATH_IF_SUPPORTED(kEmptySpan.first(1), "");
+
+  ASSERT_DEATH_IF_SUPPORTED(kEmptySpan.last(1), "");
+
+  ASSERT_DEATH_IF_SUPPORTED(kEmptySpan.subspan(1), "");
+}
+
 }  // namespace base