fix how DDC finds its undefined constant

pkg/dev_compiler/test/codegen_expected/sunflower/sunflower.js

 define(['dart_sdk'], function(dart_sdk) {
   'use strict';
   const core = dart_sdk.core;
   const html = dart_sdk.html;
   const math = dart_sdk.math;
   const dart = dart_sdk.dart;
   const dartx = dart_sdk.dartx;
   const sunflower = Object.create(null);
   const circle = Object.create(null);
   const painter = Object.create(null);
+  const $getContext = dartx.getContext;
+  const $addEventListener = dartx.addEventListener;
+  const $text = dartx.text;
+  const $arc = dartx.arc;
+  const $fill = dartx.fill;
   let StringToElement = () => (StringToElement = dart.constFn(dart.fnType(html.Element, [core.String])))();
   let EventTovoid = () => (EventTovoid = dart.constFn(dart.fnType(dart.void, [html.Event])))();
   let VoidTovoid = () => (VoidTovoid = dart.constFn(dart.fnType(dart.void, [])))();
   dart.defineLazy(sunflower, {
     get SEED_RADIUS() {
       return 2;
     },
     get SCALE_FACTOR() {
       return 4;
     },
     get MAX_D() {
       return 300;
     },
     get centerX() {
       return sunflower.MAX_D / 2;
     },
     get centerY() {
       return sunflower.centerX;
     }
   });
   sunflower.querySelector = function(selector) {
     return html.document.querySelector(selector);
   };
   dart.fn(sunflower.querySelector, StringToElement());
   dart.defineLazy(sunflower, {
     get canvas() {
       return html.CanvasElement.as(sunflower.querySelector("#canvas"));
     },
     get context() {
-      return html.CanvasRenderingContext2D.as(sunflower.canvas[dartx.getContext]('2d'));
+      return html.CanvasRenderingContext2D.as(sunflower.canvas[$getContext]('2d'));
     },
     get slider() {
       return html.InputElement.as(sunflower.querySelector("#slider"));
     },
     get notes() {
       return sunflower.querySelector("#notes");
     },
     get PHI() {
       return (math.sqrt(5) + 1) / 2;
     },
     get seeds() {
       return 0;
     },
     set seeds(_) {}
   });
   sunflower.main = function() {
-    sunflower.slider[dartx.addEventListener]('change', dart.fn(e => sunflower.draw(), EventTovoid()));
+    sunflower.slider[$addEventListener]('change', dart.fn(e => sunflower.draw(), EventTovoid()));
     sunflower.draw();
   };
   dart.fn(sunflower.main, VoidTovoid());
   sunflower.draw = function() {
     sunflower.seeds = core.int.parse(sunflower.slider.value);
     sunflower.context.clearRect(0, 0, sunflower.MAX_D, sunflower.MAX_D);
     for (let i = 0; i < dart.notNull(sunflower.seeds); i++) {
       let theta = i * painter.TAU / dart.notNull(sunflower.PHI);
       let r = math.sqrt(i) * sunflower.SCALE_FACTOR;
       let x = sunflower.centerX + r * math.cos(theta);
       let y = sunflower.centerY - r * math.sin(theta);
       new sunflower.SunflowerSeed.new(x, y, sunflower.SEED_RADIUS).draw(sunflower.context);
     }
-    sunflower.notes[dartx.text] = dart.str`${sunflower.seeds} seeds`;
+    sunflower.notes[$text] = dart.str`${sunflower.seeds} seeds`;
   };
   dart.fn(sunflower.draw, VoidTovoid());
   circle.Circle = class Circle extends core.Object {
     get x() {
       return this[x$];
     }
     set x(value) {
       super.x = value;
     }
     get y() {
       return this[y$];
     }
     set y(value) {
       super.y = value;
     }
     get radius() {
       return this[radius$];
     }
     set radius(value) {
       super.radius = value;
     }
   };
   (circle.Circle.new = function(x, y, radius) {
     this[x$] = x;
     this[y$] = y;
     this[radius$] = radius;
   }).prototype = circle.Circle.prototype;
+  dart.addTypeTests(circle.Circle);
   const x$ = Symbol("Circle.x");
   const y$ = Symbol("Circle.y");
   const radius$ = Symbol("Circle.radius");
   dart.setSignature(circle.Circle, {
     fields: () => ({
       x: dart.finalFieldType(core.num),
       y: dart.finalFieldType(core.num),
       radius: dart.finalFieldType(core.num)
     })
   });
   painter.CirclePainter = class CirclePainter extends core.Object {
     get color() {
       return this[color];
     }
     set color(value) {
       this[color] = value;
     }
     draw(context) {
       context.beginPath();
       context.lineWidth = 2;
       context.fillStyle = this.color;
       context.strokeStyle = this.color;
-      context[dartx.arc](this.x, this.y, this.radius, 0, painter.TAU, false);
-      context[dartx.fill]();
+      context[$arc](this.x, this.y, this.radius, 0, painter.TAU, false);
+      context[$fill]();
       context.closePath();
       context.stroke();
     }
   };
   (painter.CirclePainter.new = function() {
     this[color] = painter.ORANGE;
   }).prototype = painter.CirclePainter.prototype;
+  dart.addTypeTests(painter.CirclePainter);
   const color = Symbol("CirclePainter.color");
   painter.CirclePainter[dart.implements] = () => [circle.Circle];
   dart.setSignature(painter.CirclePainter, {
     fields: () => ({color: dart.fieldType(core.String)}),
     methods: () => ({draw: dart.fnType(dart.void, [html.CanvasRenderingContext2D])})
   });
   sunflower.SunflowerSeed = class SunflowerSeed extends dart.mixin(circle.Circle, painter.CirclePainter) {};
   (sunflower.SunflowerSeed.new = function(x, y, radius, color) {
     if (color === void 0) color = null;
     sunflower.SunflowerSeed.__proto__.new.call(this, x, y, radius);
     if (color != null) this.color = color;
   }).prototype = sunflower.SunflowerSeed.prototype;
+  dart.addTypeTests(sunflower.SunflowerSeed);
   dart.defineLazy(painter, {
     get ORANGE() {
       return "orange";
     },
     get RED() {
       return "red";
     },
     get BLUE() {
       return "blue";
     },
     get TAU() {
       return math.PI * 2;
     }
   });
   painter.querySelector = function(selector) {
     return html.document.querySelector(selector);
   };
   dart.fn(painter.querySelector, StringToElement());
   dart.defineLazy(painter, {
     get canvas() {
       return html.CanvasElement.as(painter.querySelector("#canvas"));
     },
     get context() {
-      return html.CanvasRenderingContext2D.as(painter.canvas[dartx.getContext]('2d'));
+      return html.CanvasRenderingContext2D.as(painter.canvas[$getContext]('2d'));
     }
   });
   dart.trackLibraries("sunflower", {
     "sunflower.dart": sunflower,
     "circle.dart": circle,
     "painter.dart": painter
   }, null);
   // Exports:
   return {
     sunflower: sunflower,
     circle: circle,
     painter: painter
   };
 });
 
 //# sourceMappingURL=sunflower.js.map