Eat all keys involving Search when ChromeVox is on and add a pass through mode command.

chrome/browser/chromeos/accessibility/spoken_feedback_event_rewriter.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/chromeos/accessibility/spoken_feedback_event_rewriter.h"
 
 #include <string>
 #include <utility>
 
 #include "ash/shell.h"
@@ skipping 35 matching lines @@
     return false;
 
   extensions::ExtensionHost* host =
       extensions::ProcessManager::Get(context)
           ->GetBackgroundHostForExtension(extension->id());
   if (!host)
     return false;
 
   content::RenderViewHost* rvh = host->render_view_host();
 
+  // Always capture the Search key.
+  capture |= key_event.IsCommandDown();
+
   // Listen for any unhandled keyboard events from ChromeVox's background page
   // when capturing keys to reinject.
   if (capture)
     host->host_contents()->SetDelegate(this);
   else
     host->host_contents()->SetDelegate(nullptr);
 
   // Forward all key events to ChromeVox's background page.
   const content::NativeWebKeyboardEvent web_event(key_event);
   rvh->GetWidget()->ForwardKeyboardEvent(web_event);
@@ skipping 71 matching lines @@
   if (delegate_->DispatchKeyEventToChromeVox(key_event, capture))
     return ui::EVENT_REWRITE_DISCARD;
   return ui::EVENT_REWRITE_CONTINUE;
 }
 
 ui::EventRewriteStatus SpokenFeedbackEventRewriter::NextDispatchEvent(
     const ui::Event& last_event,
     scoped_ptr<ui::Event>* new_event) {
   return ui::EVENT_REWRITE_CONTINUE;
 }