Re-land alexbost's experimental offscreenTabs API.

chrome/test/data/extensions/api_test/offscreen_tabs/display.js

+// Copyright (c) 2012 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 testTabs = [
+    { url: 'a.html', width: 200, height: 200 },
+    { url: 'b.html', width: 200, height: 200 }
+];
+
+var firstTabId;
+var secondTabId;
+var firstTabDataURL;
+var secondTabDataURL;
+
+var DATA_URL_PREFIX = 'data:image/png;base64,';
+
+chrome.test.runTests([
+  function createFirstTab() {
+    chrome.test.listenOnce(
+        chrome.experimental.offscreenTabs.onUpdated,
+        function(tabId, changeInfo, tab) {
+      assertSimilarTabs(testTabs[0], tab);
+      firstTabId = tab.id;
+    });
+
+    chrome.experimental.offscreenTabs.create(
+        testTabs[0], pass(function(tab) {
+      assertSimilarTabs(testTabs[0], tab);
+    }));
+  },
+
+  function createSecondTab() {
+    chrome.test.listenOnce(
+        chrome.experimental.offscreenTabs.onUpdated,
+        function(tabId, changeInfo, tab) {
+      assertSimilarTabs(testTabs[1], tab);
+      secondTabId = tab.id;
+    });
+
+    chrome.experimental.offscreenTabs.create(
+        testTabs[1], pass(function(tab) {
+      assertSimilarTabs(testTabs[1], tab);
+    }));
+  },
+
+  // Capture an image of the first tab and verify that the data URL looks
+  // reasonably correct.
+  function captureFirstTab() {
+    chrome.experimental.offscreenTabs.toDataUrl(
+        firstTabId, {format: 'png'}, pass(function(dataURL) {
+      assertEq('string', typeof(dataURL));
+      assertEq(DATA_URL_PREFIX, dataURL.substring(0, DATA_URL_PREFIX.length));
+      firstTabDataURL = dataURL;
+    }));
+  },
+
+  // Capture an image of the second tab and verify that the data URL looks
+  // reasonably correct.
+  function captureSecondTab() {
+    chrome.experimental.offscreenTabs.toDataUrl(
+        secondTabId, {format: 'png'}, pass(function(dataURL) {
+      assertEq('string', typeof(dataURL));
+      assertEq(DATA_URL_PREFIX, dataURL.substring(0, DATA_URL_PREFIX.length));
+      secondTabDataURL = dataURL;
+    }));
+  }
+
+  /*
+  This test does not work on Mac because the API always returns black images.
+
+  // Make sure the data URLs for the two tabs are different, since pages are
+  // different (though the height and widths are equal).
+  function compareCaptures() {
+    assertFalse(firstTabDataURL == secondTabDataURL);
+    chrome.test.succeed();
+  }
+  */
+]);