Implement modular compilation

test/codegen/expect/sunflower/painter.js

-dart_library.library('sunflower/painter', null, /* Imports */[
-  'dart/_runtime',
-  'dart/math',
-  'sunflower/dom',
-  'dart/core',
-  'sunflower/circle'
-], /* Lazy imports */[
-], function(exports, dart, math, dom, core, circle) {
-  'use strict';
-  let dartx = dart.dartx;
-  const ORANGE = "orange";
-  const RED = "red";
-  const BLUE = "blue";
-  const TAU = dart.notNull(math.PI) * 2;
-  function querySelector(selector) {
-    return dom.document.querySelector(selector);
-  }
-  dart.fn(querySelector, dom.Element, [core.String]);
-  dart.defineLazyProperties(exports, {
-    get canvas() {
-      return dart.as(querySelector("#canvas"), dom.CanvasElement);
-    }
-  });
-  dart.defineLazyProperties(exports, {
-    get context() {
-      return dart.as(exports.canvas.getContext('2d'), dom.CanvasRenderingContext2D);
-    }
-  });
-  class CirclePainter extends core.Object {
-    CirclePainter() {
-      this.color = ORANGE;
-    }
-    draw(context) {
-      context.beginPath();
-      context.lineWidth = 2;
-      context.fillStyle = this.color;
-      context.strokeStyle = this.color;
-      context.arc(this.x, this.y, this.radius, 0, TAU, false);
-      context.fill();
-      context.closePath();
-      context.stroke();
-    }
-  }
-  CirclePainter[dart.implements] = () => [circle.Circle];
-  dart.setSignature(CirclePainter, {
-    methods: () => ({draw: [dart.void, [dom.CanvasRenderingContext2D]]})
-  });
-  // Exports:
-  exports.ORANGE = ORANGE;
-  exports.RED = RED;
-  exports.BLUE = BLUE;
-  exports.TAU = TAU;
-  exports.querySelector = querySelector;
-  exports.CirclePainter = CirclePainter;
-});