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

chrome/renderer/plugins/chrome_plugin_placeholder.h

Index: chrome/renderer/plugins/chrome_plugin_placeholder.h
diff --git a/chrome/renderer/plugins/chrome_plugin_placeholder.h b/chrome/renderer/plugins/chrome_plugin_placeholder.h
index e174f6cb8e9e623317531c1b7eb7dd50dae67163..cfd2b7cddef847022384091b0c72acd2d7169ea8 100644
--- a/chrome/renderer/plugins/chrome_plugin_placeholder.h
+++ b/chrome/renderer/plugins/chrome_plugin_placeholder.h
@@ -8,6 +8,7 @@
 #include <stdint.h>
 
 #include "base/macros.h"
+#include "chrome/common/prerender_types.h"
 #include "chrome/renderer/plugins/power_saver_info.h"
 #include "components/plugins/renderer/loadable_plugin_placeholder.h"
 #include "content/public/renderer/context_menu_client.h"
@@ -92,6 +93,7 @@ class ChromePluginPlaceholder final
   void OnErrorDownloadingPlugin(const std::string& error);
   void OnCancelledDownloadingPlugin();
 #endif
+  void OnSetPrerenderMode(prerender::PrerenderMode mode);
 
   ChromeViewHostMsg_GetPluginInfo_Status status_;