Store LocalDefId in hir::Closure.

compiler/rustc_hir/src/hir.rs

@@ -921,6 +921,7 @@ pub struct Crate<'hir> {
 
 #[derive(Debug, HashStable_Generic)]
 pub struct Closure<'hir> {
+    pub def_id: LocalDefId,
     pub binder: ClosureBinder,
     pub capture_clause: CaptureBy,
     pub bound_generic_params: &'hir [GenericParam<'hir>],

compiler/rustc_hir/src/intravisit.rs

@@ -733,6 +733,7 @@ pub fn walk_expr<'v, V: Visitor<'v>>(visitor: &mut V, expression: &'v Expr<'v>)
             walk_list!(visitor, visit_arm, arms);
         }
         ExprKind::Closure(&Closure {
+            def_id: _,
             binder: _,
             bound_generic_params,
             fn_decl,