Use short array syntax in method signatures

test/codegen/expect/constructors.js

 var constructors = dart.defineLibrary(constructors, {});
 var core = dart.import(core);
 (function(exports, core) {
   'use strict';
   class A extends core.Object {}
   dart.setSignature(A, {});
   class B extends core.Object {
     B() {
     }
   }
@@ skipping 121 matching lines @@
         let q = new (Q$())("world");
         return dart.as(q.x, core.String);
       }
       static baz() {
         let q = new (Q$(core.int))(42);
         return dart.notNull(q.bar()) + dart.notNull(q.bar2());
       }
     }
     dart.setSignature(Q, {
       methods: () => ({
-        bar: dart.functionType(core.String, []),
-        bar2: dart.functionType(core.String, [])
+        bar: [core.String, []],
+        bar2: [core.String, []]
       }),
       statics: () => ({
-        foo: dart.functionType(Q$(), []),
-        baz: dart.functionType(core.String, [])
+        foo: [Q$(), []],
+        baz: [core.String, []]
       }),
       names: ['foo', 'baz']
     });
     return Q;
   });
   let Q = Q$();
   // Exports:
   exports.A = A;
   exports.B = B;
   exports.C = C;
   exports.C2 = C2;
   exports.D = D;
   exports.E = E;
   exports.F = F;
   exports.G = G;
   exports.H = H;
   exports.I = I;
   exports.J = J;
   exports.K = K;
   exports.L = L;
   exports.M = M;
   exports.N = N;
   exports.P = P;
   exports.Q$ = Q$;
   exports.Q = Q;
 })(constructors, core);