Support Shift+Search+Arrows to navigate and Control to silence speech everywhere

ash/shell_delegate.h

Index: ash/shell_delegate.h
diff --git a/ash/shell_delegate.h b/ash/shell_delegate.h
index c561bf1be89b33d421755b1f5cfdb22a9193589a..170ba039d52651f4e2049a8806784036d41bf5c8 100644
--- a/ash/shell_delegate.h
+++ b/ash/shell_delegate.h
@@ -191,6 +191,9 @@ class ASH_EXPORT ShellDelegate {
   // accessibility features are disabled.
   virtual bool ShouldAlwaysShowAccessibilityMenu() const = 0;
 
+  // Cancel all current and queued speech immediately.
+  virtual void SilenceSpokenFeedback() const = 0;
+
   // Invoked to create an AppListViewDelegate. Shell takes the ownership of
   // the created delegate.
   virtual app_list::AppListViewDelegate* CreateAppListViewDelegate() = 0;