check whether the printing render frame host has been initialised before accepting a message in the…

headless/lib/browser/headless_print_manager.cc

Index: headless/lib/browser/headless_print_manager.cc
diff --git a/headless/lib/browser/headless_print_manager.cc b/headless/lib/browser/headless_print_manager.cc
index 036c7471fcdc7cee8c35a46ad69b0121eb12c853..7a69f75ae0ea01c23b7c517aedea81af4ded3c04 100644
--- a/headless/lib/browser/headless_print_manager.cc
+++ b/headless/lib/browser/headless_print_manager.cc
@@ -173,6 +173,13 @@ HeadlessPrintManager::GetPrintParamsFromSettings(
 bool HeadlessPrintManager::OnMessageReceived(
     const IPC::Message& message,
     content::RenderFrameHost* render_frame_host) {
+  if (!printing_rfh_) {
+    DLOG(WARNING)
+        << "Unexpected message received before GetPDFContents is called.";
+    render_frame_host->Send(new IPC::Message());

[jzfeng, 2017/05/18 08:12:47]

use DLOG(ERROR), and add the message type into the error message, so that we
know which IPC got wrong?

Could you only send an empty reply when the IPC type is
PrintHostMsg_GetDefaultPrintSettings, or PrintHostMsg_ScriptedPrint? Looks like
other messages don't need a reply.

+    return true;
+  }
+
   bool handled = true;
   IPC_BEGIN_MESSAGE_MAP(HeadlessPrintManager, message)
     IPC_MESSAGE_HANDLER(PrintHostMsg_ShowInvalidPrinterSettingsError,