Refactor checking if a `Lifetime` is static

Simply move the test for `keywords::StaticLifetime` into the
`Lifetime` impl, to match how elision is checked.

src/librustc/hir/mod.rs

@@ -100,6 +100,10 @@ impl Lifetime {
     pub fn is_elided(&self) -> bool {
         self.name == keywords::Invalid.name()
     }
+
+    pub fn is_static(&self) -> bool {
+        self.name == keywords::StaticLifetime.name()
+    }
 }
 
 /// A lifetime definition, eg `'a: 'b+'c+'d`

src/librustc/middle/resolve_lifetime.rs

@@ -434,7 +434,7 @@ fn visit_lifetime(&mut self, lifetime_ref: &'tcx hir::Lifetime) {
             self.resolve_elided_lifetimes(slice::ref_slice(lifetime_ref));
             return;
         }
-        if lifetime_ref.name == keywords::StaticLifetime.name() {
+        if lifetime_ref.is_static() {
             self.insert_lifetime(lifetime_ref, Region::Static);
             return;
         }
@@ -1434,7 +1434,7 @@ fn check_lifetime_defs(&mut self, old_scope: ScopeRef, lifetimes: &[hir::Lifetim
             let lifetime_i = &lifetimes[i];
 
             for lifetime in lifetimes {
-                if lifetime.lifetime.name == keywords::StaticLifetime.name() {
+                if lifetime.lifetime.is_static() {
                     let lifetime = lifetime.lifetime;
                     let mut err = struct_span_err!(self.sess, lifetime.span, E0262,
                                   "invalid lifetime parameter name: `{}`", lifetime.name);