Check for warnings when loading extensions in browser tests.

chrome/test/data/extensions/api_test/icons/extension_with_permission/index.js

+var TEST_CASES = [
+  // Tests loading a standard 128px icon.
+  {
+    url: 'chrome://extension-icon/gbmgkahjioeacddebbnengilkgbkhodg/128/0',
+    expectedSize: 128
+  },
+  // Tests loading a standard 48px icon with a MATCH_SMALLER.
+  // This should not be resized to 48px.
+  {
+    url: 'chrome://extension-icon/gbmgkahjioeacddebbnengilkgbkhodg/48/2',
+    expectedSize: 32
+  },
+  // Tests loading a standard 32px icon, grayscale. We assume that we actually
+  // got a grayscale image back here.
+  {
+    url: 'chrome://extension-icon/gbmgkahjioeacddebbnengilkgbkhodg/' +
+        '32/1?grayscale=true',
+    expectedSize: 32
+  },
+  // Tests loading a 16px by resizing the 32px version (MATCH_BIGGER).
+  // This should be resized to 16px.
+  {
+    url: 'chrome://extension-icon/gbmgkahjioeacddebbnengilkgbkhodg/16/1',
+    expectedSize: 16
+  }
+];
+
+var loadedImageCount = 0;
+
+TEST_CASES.forEach(function(testCase) {
+  var img = document.createElement('img');
+  img.onload = function() {
+    if (img.naturalWidth != testCase.expectedSize ||
+        img.naturalHeight != testCase.expectedSize) {
+      document.title = 'Incorrect size on ' + testCase.url +
+          ' Expected: ' + testCase.expectedSize + 'x' + testCase.expectedSize +
+          ' Actual: ' + img.naturalWidth + 'x' + img.naturalHeight;
+      return;
+    }
+
+    if (++loadedImageCount == TEST_CASES.length) {
+      document.title = 'Loaded';
+    }
+  };
+  img.onerror = function() {
+    // We failed to load an image that should have loaded.
+    document.title = 'Couldn\'t load ' + testCase.url;
+  };
+  img.src = testCase.url;
+  document.body.appendChild(img);
+});