Fix "unused variable" warnings.

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 a1ad0ea393d63a94d1059a8a3f9c072109b7adc6..78348cf2888d7cfec090849f296d0b4591d316e3 100644
--- a/chrome/renderer/plugins/chrome_plugin_placeholder.h
+++ b/chrome/renderer/plugins/chrome_plugin_placeholder.h
@@ -112,10 +112,11 @@ class ChromePluginPlaceholder final
 #if defined(ENABLE_PLUGIN_INSTALLATION)
   // |routing_id()| is the routing ID of our associated RenderView, but we have
   // a separate routing ID for messages specific to this placeholder.
-  int32_t placeholder_routing_id_;
+  int32_t placeholder_routing_id_ = MSG_ROUTING_NONE;
+
+  bool has_host_ = false;
 #endif
 
-  bool has_host_;
   int context_menu_request_id_;  // Nonzero when request pending.
   base::string16 plugin_name_;