Reland "Add accessibility alert event when DeepScanningDialogViews changes"

This is a reland of 2e94ca8d that just
disables the failing assertion on Mac until the root cause is figured
out.

Original change's description:
> Add accessibility alert event when DeepScanningDialogViews changes
>
> This allows a screen reader to read the updated text of the dialog.
>
> Bug: 1131565
> Change-Id: I73a2df8067ffc96148ebf5d50a9412cf34b67feb
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2424841
> Commit-Queue: Dominique Fauteux-Chapleau <domfc@chromium.org>
> Reviewed-by: Roger Tawa <rogerta@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#810290}

TBR=rogerta@chromium.org,dmazzoni@chromium.org

Bug: 1131565
Change-Id: If8ba41e1490e9cfa0013fc4de145bbdebebc1c45
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2431785Reviewed-by: Dominique Fauteux-Chapleau <domfc@chromium.org>
Commit-Queue: Dominique Fauteux-Chapleau <domfc@chromium.org>
Cr-Commit-Position: refs/heads/master@{#810802}

chrome/browser/safe_browsing/cloud_content_scanning/deep_scanning_dialog_views.cc

@@ -27,6 +27,7 @@
 #include "ui/gfx/paint_vector_icon.h"
 #include "ui/gfx/text_constants.h"
 #include "ui/native_theme/native_theme.h"
+#include "ui/views/accessibility/view_accessibility.h"
 #include "ui/views/background.h"
 #include "ui/views/border.h"
 #include "ui/views/bubble/bubble_frame_view.h"
@@ -351,8 +352,11 @@ void DeepScanningDialogViews::UpdateDialog() {
   // Update the buttons.
   SetupButtons();
 
-  // Update the message's text.
-  message_->SetText(GetDialogMessage());
+  // Update the message's text, and send an alert for screen readers since the
+  // text changed.
+  base::string16 new_message = GetDialogMessage();
+  message_->SetText(new_message);
+  message_->GetViewAccessibility().AnnounceText(std::move(new_message));
 
   // Resize the dialog's height. This is needed since the text might take more
   // lines after changing.

chrome/browser/safe_browsing/cloud_content_scanning/deep_scanning_dialog_views_browsertest.cc

@@ -22,6 +22,7 @@
 #include "ui/base/resource/resource_bundle.h"
 #include "ui/views/controls/image_view.h"
 #include "ui/views/controls/throbber.h"
+#include "ui/views/test/ax_event_counter.h"
 
 namespace safe_browsing {
 
@@ -41,13 +42,15 @@ base::string16 text() {
 // - It respects time constraints (minimum shown time, initial delay, timeout)
 // - It is always destroyed, therefore |quit_closure_| is called in the dtor
 //   observer.
+// - It sends accessibility events correctly.
 class DeepScanningDialogViewsBehaviorBrowserTest
     : public DeepScanningBrowserTestBase,
       public DeepScanningDialogViews::TestObserver,
       public testing::WithParamInterface<
           std::tuple<bool, bool, base::TimeDelta>> {
  public:
-  DeepScanningDialogViewsBehaviorBrowserTest() {
+  DeepScanningDialogViewsBehaviorBrowserTest()
+      : ax_event_counter_(views::AXEventManager::Get()) {
     DeepScanningDialogViews::SetObserverForTesting(this);
 
     expected_scan_result_ = dlp_success() && malware_success();
@@ -86,6 +89,11 @@ class DeepScanningDialogViewsBehaviorBrowserTest
     // The dialog's buttons should be Cancel in the pending and fail case.
     EXPECT_EQ(dialog_->GetDialogButtons(), ui::DIALOG_BUTTON_CANCEL);
 
+    // Record the number of AX events until now to check if the text update adds
+    // one later.
+    ax_events_count_when_first_shown_ =
+        ax_event_counter_.GetCount(ax::mojom::Event::kAlert);
+
     // The dialog should only be shown once some time after being constructed.
     EXPECT_TRUE(ctor_called_);
     EXPECT_FALSE(views_first_shown_);
@@ -122,6 +130,14 @@ class DeepScanningDialogViewsBehaviorBrowserTest
     // The dialog should only be updated once some time after being shown.
     EXPECT_TRUE(views_first_shown_);
     EXPECT_FALSE(dialog_updated_);
+
+    // TODO(crbug/1131565): Re-enable this for Mac.
+#if !defined(OS_MAC)
+    // The dialog being updated implies an accessibility alert is sent.
+    EXPECT_EQ(ax_events_count_when_first_shown_ + 1,
+              ax_event_counter_.GetCount(ax::mojom::Event::kAlert));
+#endif
+
     dialog_updated_ = true;
   }
 
@@ -178,6 +194,9 @@ class DeepScanningDialogViewsBehaviorBrowserTest
   bool dialog_updated_ = false;
 
   bool expected_scan_result_;
+
+  int ax_events_count_when_first_shown_ = 0;
+  views::test::AXEventCounter ax_event_counter_;
 };
 
 // Tests the behavior of the dialog in the following ways: