[Locked Fullscreen] Disable ChromeVox panel before entering locked fullscreen

There's a P0 escape from the locked mode currently in M75 which is just days
away from stable.  This is a very quick and simple fix that addresses the
problem for now and it will be backmerged immediately to M75.

Bug: 957950
Change-Id: I2c39c04d4bc0219c000977928b538c60619a6bf6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1632251
Commit-Queue: Ivan Šandrk <isandrk@chromium.org>
Reviewed-by: Kush Sinha <sinhak@chromium.org>
Cr-Commit-Position: refs/heads/master@{#663763}

chrome/browser/extensions/api/tabs/tabs_util_chromeos.cc

@@ -7,6 +7,7 @@
 #include "ash/public/cpp/window_properties.h"
 #include "ash/public/interfaces/window_pin_type.mojom.h"
 #include "base/metrics/histogram_macros.h"
+#include "chrome/browser/chromeos/accessibility/accessibility_manager.h"
 #include "chrome/browser/chromeos/arc/arc_session_manager.h"
 #include "chrome/browser/chromeos/arc/arc_util.h"
 #include "chrome/browser/chromeos/arc/voice_interaction/voice_interaction_controller_client.h"
@@ -27,6 +28,14 @@ namespace tabs_util {
 void SetLockedFullscreenState(Browser* browser, bool locked) {
   UMA_HISTOGRAM_BOOLEAN("Extensions.LockedFullscreenStateRequest", locked);
 
+  // Disable ChromeVox before entering locked fullscreen.  Quickfix for
+  // crbug.com/957950.
+  auto* const accessibility_manager = chromeos::AccessibilityManager::Get();
+  if (locked && accessibility_manager &&
+      accessibility_manager->IsSpokenFeedbackEnabled()) {
+    accessibility_manager->EnableSpokenFeedback(false);
+  }
+
   aura::Window* window = browser->window()->GetNativeWindow();
   // TRUSTED_PINNED is used here because that one locks the window fullscreen
   // without allowing the user to exit (as opposed to regular PINNED).