DevTools: allow embedder handling async remote debugger commands.

content/browser/devtools/protocol/page_handler.cc

Index: content/browser/devtools/protocol/page_handler.cc
diff --git a/content/browser/devtools/protocol/page_handler.cc b/content/browser/devtools/protocol/page_handler.cc
index 740c0a2bf3d7150c57eed70a7ede306d52ad8bf5..243fd2dd524bf7e98e0f09798db3491f7e254ed4 100644
--- a/content/browser/devtools/protocol/page_handler.cc
+++ b/content/browser/devtools/protocol/page_handler.cc
@@ -296,6 +296,11 @@ void PageHandler::CaptureScreenshot(
                  screenshot_quality));
 }
 
+void PageHandler::PrintToPDF(std::unique_ptr<PrintToPDFCallback> callback) {
+  callback->sendFailure(Response::Error("PrintToPDF is not implemented"));
+  return;
+}
+
 Response PageHandler::StartScreencast(Maybe<std::string> format,
                                       Maybe<int> quality,
                                       Maybe<int> max_width,