Use signature inheritance when method types are unchanged

test/codegen/expect/DeltaBlue.js

 var DeltaBlue = dart.defineLibrary(DeltaBlue, {});
 var BenchmarkBase = dart.import(BenchmarkBase);
 var core = dart.import(core);
 (function(exports, BenchmarkBase, core) {
   'use strict';
   function main() {
     new DeltaBlue().report();
   }
   dart.fn(main);
   class DeltaBlue extends BenchmarkBase.BenchmarkBase {
     DeltaBlue() {
       super.BenchmarkBase("DeltaBlue");
     }
     run() {
       chainTest(100);
       projectionTest(100);
     }
   }
-  dart.setSignature(DeltaBlue, {
-    methods: () => ({run: dart.functionType(dart.void, [])})
-  });
+  dart.setSignature(DeltaBlue, {});
   class Strength extends core.Object {
     Strength(value, name) {
       this.value = value;
       this.name = name;
     }
     nextWeaker() {
       return dart.const(dart.setType([STRONG_PREFERRED, PREFERRED, STRONG_DEFAULT, NORMAL, WEAK_DEFAULT, WEAKEST], core.List$(Strength)))[core.$get](this.value);
     }
     static stronger(s1, s2) {
       return dart.notNull(s1.value) < dart.notNull(s2.value);
@@ skipping 133 matching lines @@
   class EditConstraint extends UnaryConstraint {
     EditConstraint(v, str) {
       super.UnaryConstraint(v, str);
     }
     isInput() {
       return true;
     }
     execute() {}
   }
   dart.setSignature(EditConstraint, {
-    methods: () => ({
-      isInput: dart.functionType(core.bool, []),
-      execute: dart.functionType(dart.void, [])
-    })
+    methods: () => ({execute: dart.functionType(dart.void, [])})
   });
   let NONE = 1;
   let FORWARD = 2;
   let BACKWARD = 0;
   class BinaryConstraint extends Constraint {
     BinaryConstraint(v1, v2, strength) {
       this.v1 = v1;
       this.v2 = v2;
       this.direction = NONE;
       super.Constraint(strength);
@@ skipping 96 matching lines @@
     }
     recalculate() {
       let ihn = this.input(), out = this.output();
       out.walkStrength = Strength.weakest(this.strength, ihn.walkStrength);
       out.stay = dart.notNull(ihn.stay) && dart.notNull(this.scale.stay) && dart.notNull(this.offset.stay);
       if (out.stay)
         this.execute();
     }
   }
   dart.setSignature(ScaleConstraint, {
-    methods: () => ({
-      addToGraph: dart.functionType(dart.void, []),
-      removeFromGraph: dart.functionType(dart.void, []),
-      markInputs: dart.functionType(dart.void, [core.int]),
-      execute: dart.functionType(dart.void, []),
-      recalculate: dart.functionType(dart.void, [])
-    })
+    methods: () => ({execute: dart.functionType(dart.void, [])})
   });
   class EqualityConstraint extends BinaryConstraint {
     EqualityConstraint(v1, v2, strength) {
       super.BinaryConstraint(v1, v2, strength);
     }
     execute() {
       this.output().value = this.input().value;
     }
   }
   dart.setSignature(EqualityConstraint, {
@@ skipping 244 matching lines @@
   exports.BinaryConstraint = BinaryConstraint;
   exports.ScaleConstraint = ScaleConstraint;
   exports.EqualityConstraint = EqualityConstraint;
   exports.Variable = Variable;
   exports.Planner = Planner;
   exports.Plan = Plan;
   exports.chainTest = chainTest;
   exports.projectionTest = projectionTest;
   exports.change = change;
 })(DeltaBlue, BenchmarkBase, core);