Add a WebContentsImpl API to snapshot the accessibility tree.

content/browser/accessibility/snapshot_ax_tree_browsertest.cc

+// Copyright 2015 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.
+
+#include "base/callback.h"
+#include "content/browser/web_contents/web_contents_impl.h"
+#include "content/public/test/content_browser_test.h"
+#include "content/public/test/content_browser_test_utils.h"
+#include "content/public/test/test_utils.h"
+#include "content/shell/browser/shell.h"
+#include "testing/gtest/include/gtest/gtest.h"
+#include "ui/accessibility/ax_node.h"
+#include "ui/accessibility/ax_tree.h"
+
+namespace content {
+
+namespace {
+
+class AXTreeSnapshotWaiter {
+ public:
+  AXTreeSnapshotWaiter() : loop_runner_(new MessageLoopRunner()) {}
+
+  void Wait() {
+    loop_runner_->Run();
+  }
+
+  const ui::AXTreeUpdate& snapshot() const { return snapshot_; }
+
+  void ReceiveSnapshot(const ui::AXTreeUpdate& snapshot) {
+    snapshot_ = snapshot;
+    loop_runner_->Quit();
+  }
+
+ private:
+  ui::AXTreeUpdate snapshot_;
+  scoped_refptr<MessageLoopRunner> loop_runner_;
+
+  DISALLOW_COPY_AND_ASSIGN(AXTreeSnapshotWaiter);
+};
+
+}  // namespace
+
+class SnapshotAXTreeBrowserTest : public ContentBrowserTest {
+ public:
+  SnapshotAXTreeBrowserTest() {}
+  ~SnapshotAXTreeBrowserTest() override {}
+};
+
+IN_PROC_BROWSER_TEST_F(SnapshotAXTreeBrowserTest,
+                       SnapshotAccessibilityTreeFromWebContents) {
+  const char url_str[] = "data:text/html,<button>Click</button>";

[Charlie Reis, 2015/04/02 23:09:06]

Just curious, why the char[]?  I would normally expect std::string or just
inlining this into the next line's GURL constructor, but I'm open to learning
reasons to use C style strings.

[dmazzoni, 2015/04/03 22:49:41]

No preference - I forked this from another test where it may have made sense to
have the url for some reason.

I inlined it into the GURL constructor.

+  GURL url(url_str);
+  NavigateToURL(shell(), url);
+
+  WebContentsImpl* web_contents =
+      static_cast<WebContentsImpl*>(shell()->web_contents());
+
+  AXTreeSnapshotWaiter waiter;
+  web_contents->RequestAXTreeSnapshot(
+      base::Bind(&AXTreeSnapshotWaiter::ReceiveSnapshot,
+                 base::Unretained(&waiter)));
+  waiter.Wait();
+
+  LOG(INFO) << waiter.snapshot().ToString();

[Charlie Reis, 2015/04/02 23:09:06]

LOG(INFO) isn't allowed in new code anymore, is it?  Looks like it's very rare
now.

[dmazzoni, 2015/04/03 22:49:41]

It's banned for browser code, but I don't think it's banned for tests. Here's my
reasoning behind leaving it here: if the test passes, you won't see it either
way so it doesn't matter. But if the test fails, this debug string will give you
a lot of insight into *why* it failed. Making it VLOG(1) could work for
debugging a test locally, but that's not helpful if six months from now it
starts failing on a builder or try bot.

I guess one alternative would be to somehow trigger the log only if the test
fails - do you know if there's any way to do that?

[Charlie Reis, 2015/04/06 21:56:50]

You can send it into a particular ASSERT_EQ statement with <<:
https://code.google.com/p/googletest/wiki/Primer#Assertions

That said, Paweł would know better than I would what the best practice for this
is.

[dmazzoni, 2015/04/09 18:39:01]

Great, idea, done.

+
+  ui::AXTree tree(waiter.snapshot());
+  ui::AXNode* root = tree.root();
+  ASSERT_EQ(ui::AX_ROLE_ROOT_WEB_AREA, root->data().role);
+  ui::AXNode* group = root->ChildAtIndex(0);
+  ASSERT_EQ(ui::AX_ROLE_GROUP, group->data().role);
+  ui::AXNode* button = group->ChildAtIndex(0);
+  ASSERT_EQ(ui::AX_ROLE_BUTTON, button->data().role);
+}
+
+}  // namespace content