Initialize initial AX tree after BrowserAccessibilityManagerWin.

This was a subtle bug - the initial AX tree was being initialized
in the BrowserAccessibilityManager constructor, before the subclass,
BrowserAccessibilityManagerWin, was constructed. That meant that
BrowserAccessibilityManagerWin overrides were not being called,
so the native Win objects for the initial tree were not working.
In particular, BrowserAccessibilityManagerWin::OnNodeCreated
wasn't getting called, so the mapping from Windows unique ids
to objects wasn't getting initialized.

The user impact of this is that when loading a new URL, NVDA would
sometimes announce "Unknown"  - this is because it'd get events on
the initial document (before the real page loads), but attempts to
query that initial document would fail.

Adds a unit test to demonstrate exactly what failed and prevent it
from regressing.

BUG=421116

Review URL: https://codereview.chromium.org/631223005

Cr-Commit-Position: refs/heads/master@{#298573}

1 files changed, 2 insertions, 1 deletions

diff --git a/content/browser/accessibility/browser_accessibility_manager_android.cc b/content/browser/accessibility/browser_accessibility_manager_android.cc
index e878e6c..678bd69 100644
--- a/content/browser/accessibility/browser_accessibility_manager_android.cc
+++ b/content/browser/accessibility/browser_accessibility_manager_android.cc
@@ -74,8 +74,9 @@ BrowserAccessibilityManagerAndroid::BrowserAccessibilityManagerAndroid(
     const ui::AXTreeUpdate& initial_tree,
     BrowserAccessibilityDelegate* delegate,
     BrowserAccessibilityFactory* factory)
-    : BrowserAccessibilityManager(initial_tree, delegate, factory) {
+    : BrowserAccessibilityManager(delegate, factory) {
   SetContentViewCore(content_view_core);
+  Initialize(initial_tree);
 }
 
 BrowserAccessibilityManagerAndroid::~BrowserAccessibilityManagerAndroid() {