Enable keyboard accelerator for GetHelp in Ash.
In the past the accelerator is handled at browser level so doesn't work
if no browser window present.

BUG=321568

Review URL: https://codereview.chromium.org/827253002

Cr-Commit-Position: refs/heads/master@{#310485}
diff --git a/ash/shell/shell_delegate_impl.cc b/ash/shell/shell_delegate_impl.cc
index c9de885..dc081c6 100644
--- a/ash/shell/shell_delegate_impl.cc
+++ b/ash/shell/shell_delegate_impl.cc
@@ -45,6 +45,7 @@
   }
   void OpenFileManager() override {}
   void OpenCrosh() override {}
+  void OpenGetHelp() override {}
   void RestoreTab() override {}
   void ShowKeyboardOverlay() override {}
   void ShowTaskManager() override {}