Mark 'front()' and 'back()' as noexcept for array/deque/string/string_view. These are just rebranded 'operator[]', and should be noexcept like it is.

llvm-svn: 356435
Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: 9ea0e473f0b96455b918eefcf8fc535638674a1f
diff --git a/include/string_view b/include/string_view
index 79565c2..9a6eb0c 100644
--- a/include/string_view
+++ b/include/string_view
@@ -288,13 +288,13 @@
     }
 
     _LIBCPP_CONSTEXPR _LIBCPP_INLINE_VISIBILITY
-    const_reference front() const
+    const_reference front() const _NOEXCEPT
     {
         return _LIBCPP_ASSERT(!empty(), "string_view::front(): string is empty"), __data[0];
     }
 
     _LIBCPP_CONSTEXPR _LIBCPP_INLINE_VISIBILITY
-    const_reference back() const
+    const_reference back() const _NOEXCEPT
     {
         return _LIBCPP_ASSERT(!empty(), "string_view::back(): string is empty"), __data[__size-1];
     }