Get rid of AX_LINE_BREAKS attribute to improve performance.

chrome/test/data/extensions/api_test/automation/tests/tabs/line_start_offsets.js

Index: chrome/test/data/extensions/api_test/automation/tests/tabs/line_start_offsets.js
diff --git a/chrome/test/data/extensions/api_test/automation/tests/tabs/line_start_offsets.js b/chrome/test/data/extensions/api_test/automation/tests/tabs/line_start_offsets.js
new file mode 100644
index 0000000000000000000000000000000000000000..994241967c67f6cc05351ae8d0143734d9e11e5c
--- /dev/null
+++ b/chrome/test/data/extensions/api_test/automation/tests/tabs/line_start_offsets.js
@@ -0,0 +1,29 @@
+// Copyright 2016 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 allTests = [
+  function testInput() {
+    var input = rootNode.firstChild.firstChild;

[dmazzoni, 2016/09/13 17:29:38]

This is fragile, anytime we change what nodes are ignored the test will have to
be updated.

Do something like this instead:

  var input = rootNode.find({ role: 'textField' });

You can also find by name or almost any other attribute so you can find both

+    rootNode.addEventListener(
+        EventType.childrenChanged, function(e) {

[dmazzoni, 2016/09/13 17:29:38]

Why are you running this on childrenChanged? Is the test failing if you run it
on page load? I'm surprised if so.

It seems to me like this test will probably be flaky because there's no
guarantee you'll get a childrenChanged every time this page loads

+          var line_starts = input.lineStartOffsets();
+          assertNotNull(lineStarts);
+          assertEq(1, line_starts.length());
+          assertEq(0, line_starts[i]);
+        });
+  },
+
+  function testTextarea() {
+    var input = rootNode.firstChild.firstChild;
+    rootNode.addEventListener(
+        EventType.childrenChanged, function(e) {
+          var line_starts = textarea.lineStartOffsets();
+          assertNotNull(lineStarts);
+          assertEq(3, line_starts.length());
+          assertEq(0, line_starts[i]);
+        });
+  }
+];
+
+setUpAndRunTests(allTests);