Fix bugs in sheriff-o-matic's pixel zoomer.

Tools/GardeningServer/ui/ct-results-comparison-zoomer-tests.html

 <!--
 Copyright 2014 The Chromium Authors. All rights reserved.
 Use of this source code is governed by a BSD-style license that can be
 found in the LICENSE file.
 -->
 
 <link rel="import" href="ct-results-comparison-zoomer.html">
 
+<link rel="import" href="../base/ct-canvas-2d-context-mock.html">
+
 <script>
 (function () {
 
 module("ct-results-comparison-zoomer");
 
 asyncTest("no-position", 2, function() {
   var zoomer = document.createElement('ct-results-comparison-zoomer');
   // FIXME: This should set zoomer.position instead, but there's no way
   // to get between the microtask and requestAnimationFrame to verify the
   // behavior.
@@ skipping 29 matching lines @@
   }
 
   try {
     zoomer._draw(zoomer.$.diffZoomer);
     ok(true);
   } catch(e) {
     ok(false);
   }
 });
 
+asyncTest("drawCanvas", 1, function() {
+  var zoomer = document.createElement('ct-results-comparison-zoomer');
+  zoomer.position = {x: 0.2, y: 0.5};
+
+  requestAnimationFrame(function() {
+    var canvasContext = new CTCanvas2dContextMock();
+    zoomer._drawCanvas(canvasContext, zoomer.$.diffZoomer);
+
+    var expectedContext = new CTCanvas2dContextMock();
+    expectedContext.imageSmoothingEnabled = false;
+    expectedContext.translate(-960, -1800);
+    expectedContext.strokeRect(-1.5, -1.5, 4802, 3602);
+    expectedContext.scale(6, 6);
+    expectedContext.drawImage(zoomer.shadowRoot.querySelector('img'), 0, 0);
+    deepEqual(canvasContext, expectedContext);
+    start();
+  });
+});
+
 })()
 </script>