Enable noexcept on Windows, use for a few move constructors.

base/containers/flat_tree.h

Index: base/containers/flat_tree.h
diff --git a/base/containers/flat_tree.h b/base/containers/flat_tree.h
index 57335d8882b0268fb6d607595b4bec9579f27c55..6fe2bf3c5ba1d6835060f49080538b9130ea43f3 100644
--- a/base/containers/flat_tree.h
+++ b/base/containers/flat_tree.h
@@ -82,7 +82,7 @@ class flat_tree {
             const key_compare& comp = key_compare());
 
   flat_tree(const flat_tree&);
-  flat_tree(flat_tree&&);
+  flat_tree(flat_tree&&) noexcept;
 
   // Not stable in the presence of duplicates in the initializer list.
   flat_tree(std::initializer_list<value_type> ilist,
@@ -335,8 +335,8 @@ flat_tree<Key, Value, GetKeyFromValue, KeyCompare>::flat_tree(
     const flat_tree&) = default;
 
 template <class Key, class Value, class GetKeyFromValue, class KeyCompare>
-flat_tree<Key, Value, GetKeyFromValue, KeyCompare>::flat_tree(flat_tree&&) =
-    default;
+flat_tree<Key, Value, GetKeyFromValue, KeyCompare>::flat_tree(
+    flat_tree&&) noexcept = default;
 
 template <class Key, class Value, class GetKeyFromValue, class KeyCompare>
 flat_tree<Key, Value, GetKeyFromValue, KeyCompare>::flat_tree(