[Prerender] Change IPC from bool to enum for more prerender modes

chrome/renderer/prerender/prerender_helper.cc

 // Copyright (c) 2012 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/renderer/prerender/prerender_helper.h"
 
 #include "base/metrics/field_trial.h"
 #include "base/metrics/histogram.h"
 #include "chrome/common/prerender_messages.h"
 #include "content/public/renderer/document_state.h"
@@ skipping 40 matching lines @@
 bool PrerenderHelper::OnMessageReceived(
     const IPC::Message& message) {
   IPC_BEGIN_MESSAGE_MAP(PrerenderHelper, message)
     IPC_MESSAGE_HANDLER(PrerenderMsg_SetIsPrerendering, OnSetIsPrerendering)
   IPC_END_MESSAGE_MAP()
   // Return false on PrerenderMsg_SetIsPrerendering so other observers can see
   // the message.
   return false;
 }
 
-void PrerenderHelper::OnSetIsPrerendering(bool is_prerendering) {
+void PrerenderHelper::OnSetIsPrerendering(PrerenderMode mode) {
   // Immediately after construction, |this| may receive the message that
   // triggered its creation.  If so, ignore it.
-  if (is_prerendering)
+  if (mode != prerender::NO_PRERENDER)
     return;
 
   content::RenderFrame* frame = render_frame();
   // |this| must be deleted so PrerenderHelper::IsPrerendering returns false
   // when the visibility state is updated, so the visibility state string will
   // not be "prerendered".
   delete this;
 
   UpdateVisibilityState(frame);
 }
 
 void PrerenderHelper::OnDestruct() {
   delete this;
 }
 
 }  // namespace prerender