Add some missing ENABLE_PLUGINS ifdefs.

content/common/frame_messages.h

Index: content/common/frame_messages.h
diff --git a/content/common/frame_messages.h b/content/common/frame_messages.h
index 1d9be84746a0118baef26b39d2f79dd6ea2d271e..d9a7ea6fcefb49840b8895f2793f6bb45b596290 100644
--- a/content/common/frame_messages.h
+++ b/content/common/frame_messages.h
@@ -600,6 +600,7 @@ IPC_MESSAGE_ROUTED2(FrameHostMsg_DomOperationResponse,
                     std::string  /* json_string */,
                     int  /* automation_id */)
 
+#if defined(ENABLE_PLUGINS)
 // Sent to the browser when the renderer detects it is blocked on a pepper
 // plugin message for too long. This is also sent when it becomes unhung
 // (according to the value of is_hung). The browser can give the user the
@@ -643,6 +644,8 @@ IPC_SYNC_MESSAGE_CONTROL4_2(FrameHostMsg_OpenChannelToPlugin,
                             IPC::ChannelHandle /* channel_handle */,
                             content::WebPluginInfo /* info */)
 
+#endif  // defined(ENABLE_PLUGINS)
+
 // Acknowledge that we presented an ubercomp frame.
 //
 // See FrameMsg_CompositorFrameSwapped