add print to pdf for headless

components/printing/renderer/print_web_view_helper_mac.mm

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "components/printing/renderer/print_web_view_helper.h"
 
 #import <AppKit/AppKit.h>
 
 #include "base/logging.h"
 #include "base/mac/scoped_nsautorelease_pool.h"
@@ skipping 12 matching lines @@
                                           int page_count) {
   const PrintMsg_PrintPages_Params& params = *print_pages_params_;
   const PrintMsg_Print_Params& print_params = params.params;
 
   std::vector<int> printed_pages = GetPrintedPages(params, page_count);
   if (printed_pages.empty())
     return false;
 
   PrintMsg_PrintPage_Params page_params;
   page_params.params = print_params;
-  for (int page_number : printed_pages) {
-    page_params.page_number = page_number;
-    PrintPageInternal(page_params, frame);
+
+  if (delegate_->UseSingleMetafile()) {
+    PrintPagesInternal(page_params, frame, printed_pages);
+    return true;
   }
+
+  for (int page_number : printed_pages)
+    PrintPagesInternal(page_params, frame, std::vector<int>{page_number});
   return true;
 }
 #endif  // BUILDFLAG(ENABLE_BASIC_PRINTING)
 
-void PrintWebViewHelper::PrintPageInternal(
+void PrintWebViewHelper::PrintPagesInternal(
     const PrintMsg_PrintPage_Params& params,
-    blink::WebLocalFrame* frame) {
+    blink::WebLocalFrame* frame,
+    const std::vector<int>& printed_pages) {
   PdfMetafileSkia metafile(PDF_SKIA_DOCUMENT_TYPE);
   CHECK(metafile.Init());
 
-  int page_number = params.page_number;
   gfx::Size page_size_in_dpi;
   gfx::Rect content_area_in_dpi;
-  RenderPage(print_pages_params_->params, page_number, frame, false, &metafile,
-             &page_size_in_dpi, &content_area_in_dpi);
+  for (int page_number : printed_pages) {
+    RenderPage(params.params, page_number, frame, false, &metafile,
+               &page_size_in_dpi, &content_area_in_dpi);
+  }
   metafile.FinishDocument();
 
   PrintHostMsg_DidPrintPage_Params page_params;
   page_params.data_size = metafile.GetDataSize();
-  page_params.page_number = page_number;
   page_params.document_cookie = params.params.document_cookie;
   page_params.page_size = page_size_in_dpi;
   page_params.content_area = content_area_in_dpi;
 
   // Ask the browser to create the shared memory for us.
   if (!CopyMetafileDataToSharedMem(metafile,
                                    &(page_params.metafile_data_handle))) {
     // TODO(thestig): Fail and return false instead.
     page_params.data_size = 0;
   }
 
-  Send(new PrintHostMsg_DidPrintPage(routing_id(), page_params));
+  for (int page_number : printed_pages) {
+    page_params.page_number = page_number;
+    Send(new PrintHostMsg_DidPrintPage(routing_id(), page_params));
+    page_params.metafile_data_handle = base::SharedMemoryHandle();

[hal.canary, 2017/04/24 20:07:54]

What does line 76 do here?

Why do pages after the first one send a different value of
page_params.metafile_data_handle ?

[Lei Zhang, 2017/04/24 21:30:05]

Only the first page contains real data. The rest are just dummy messages to
satisfy the browser's expectations. See UseSingleMetafile() and related
modifications.

+  }
 }
 
 #if BUILDFLAG(ENABLE_PRINT_PREVIEW)
 bool PrintWebViewHelper::RenderPreviewPage(
     int page_number,
     const PrintMsg_Print_Params& print_params) {
   PrintMsg_Print_Params printParams = print_params;
   std::unique_ptr<PdfMetafileSkia> draft_metafile;
   PdfMetafileSkia* initial_render_metafile = print_preview_context_.metafile();
 
@@ skipping 72 matching lines @@
 #endif  // BUILDFLAG(ENABLE_PRINT_PREVIEW)
     RenderPageContent(frame, page_number, canvas_area, content_area,
                       scale_factor, static_cast<blink::WebCanvas*>(canvas));
   }
 
   // Done printing. Close the device context to retrieve the compiled metafile.
   metafile->FinishPage();
 }
 
 }  // namespace printing