Exposes the accessibility ID for each View

Every accessibility object has an ID that is used to identify the object
in accessibility events, calls to methods that navigate the accessibility tree,
such as IAccessible::get_accChild and get_accParent, etc.
Before this patch, we were erroniously exposing an ID of -1 in the accessibility data
of every View instead of its correct ID.
R=aleventhal@chromium.org

Change-Id: I77f31c2a3c0138ff505ff386999c60bf7465fac1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1907428Reviewed-by: Aaron Leventhal <aleventhal@chromium.org>
Commit-Queue: Nektarios Paisios <nektar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#714008}

ui/views/accessibility/view_accessibility.cc

@@ -119,6 +119,8 @@ const ui::AXUniqueId& ViewAccessibility::GetUniqueId() const {
 }
 
 void ViewAccessibility::GetAccessibleNodeData(ui::AXNodeData* data) const {
+  data->id = GetUniqueId().Get();
+
   // Views may misbehave if their widget is closed; return an unknown role
   // rather than possibly crashing.
   const views::Widget* widget = view_->GetWidget();