Fixes potential crash when toggling accessibility services

Bug: 887235
Change-Id: Id5aed4e8030ae0d8db02d369bf61772444b441ad
Reviewed-on: https://chromium-review.googlesource.com/c/1286905
Commit-Queue: David Tseng <dtseng@chromium.org>
Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#600924}

chrome/browser/chromeos/accessibility/spoken_feedback_event_rewriter_delegate.cc

@@ -35,6 +35,9 @@ void SpokenFeedbackEventRewriterDelegate::DispatchKeyEventToChromeVox(
     bool capture) {
   extensions::ExtensionHost* host = chromeos::GetAccessibilityExtensionHost(
       extension_misc::kChromeVoxExtensionId);
+  if (!host)
+    return;
+
   // Listen for any unhandled keyboard events from ChromeVox's background page
   // when capturing keys to reinject.
   host->host_contents()->SetDelegate(capture ? this : nullptr);
@@ -47,6 +50,9 @@ void SpokenFeedbackEventRewriterDelegate::DispatchMouseEventToChromeVox(
     std::unique_ptr<ui::Event> event) {
   extensions::ExtensionHost* host = chromeos::GetAccessibilityExtensionHost(
       extension_misc::kChromeVoxExtensionId);
+  if (!host)
+    return;
+
   // Forward the event to ChromeVox's background page.
   chromeos::ForwardMouseToExtension(*(event->AsMouseEvent()), host);
 }

chrome/browser/chromeos/accessibility/switch_access_event_handler.cc

@@ -51,6 +51,9 @@ void SwitchAccessEventHandler::DispatchKeyEventToSwitchAccess(
     const ui::KeyEvent& event) {
   extensions::ExtensionHost* host =
       GetAccessibilityExtensionHost(extension_misc::kSwitchAccessExtensionId);
+  if (!host)
+    return;
+
   ForwardKeyToExtension(event, host);
 }