Fix the dynamic browser action setIcon path to work with any size icon.

chrome/test/data/extensions/api_test/browser_action/no_icon/background.js

 // Copyright (c) 2011 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.
 
 var canvas = document.getElementById("canvas").getContext('2d').
-    getImageData(0, 0, 19, 19);
+    getImageData(0, 0, 21, 21);

[Devlin, 2016/01/13 19:58:12]

Were these chosen as sizes that are unused?

[Evan Stade, 2016/01/14 01:59:19]

yea, pretty much arbitrary. As the comment in the test states, I didn't want x /
16 or x / 19 to come out to a scale factor that's likely to appear on any device
that might run these tests, because then the tests are not as easy to write (as
representations will get automatically added for the active scale factor, so
testing their non-existence doesn't work).

 var canvasHD = document.getElementById("canvas").getContext('2d').
-    getImageData(0, 0, 38, 38);
+    getImageData(0, 0, 42, 42);
 
 var setIconParamQueue = [
   {imageData: canvas},
   {path: 'icon.png'},
-  {imageData: {'19': canvas, '38': canvasHD}},
-  {path: {'19': 'icon.png', '38': 'icon.png'}},
-  {imageData: {'19': canvas}},
-  {path: {'19': 'icon.png'}},
-  {imageData: {'38': canvasHD}},
+  {imageData: {'21': canvas, '42': canvasHD}},
+  {path: {'21': 'icon.png', '42': 'icon.png'}},
+  {imageData: {'21': canvas}},
+  {path: {'21': 'icon.png'}},
+  {imageData: {'42': canvasHD}},
   {imageData: {}},
   {path: {}},
 ];
 
 // Called when the user clicks on the browser action.
 chrome.browserAction.onClicked.addListener(function(windowId) {
   if (setIconParamQueue.length == 0) {
     chrome.test.notifyFail("Queue of params for test cases unexpectedly empty");
     return;
   }
 
   try {
     chrome.browserAction.setIcon(setIconParamQueue.shift(), function() {
       chrome.test.notifyPass();});
   } catch (error) {
     console.log(error.message);
     chrome.test.notifyFail(error.message);
   }
 });
 
 chrome.test.notifyPass();