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,
+    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;

[Lei Zhang, 2017/04/06 08:08:42]

In principle, due to fancy CSS, this can be different per page. e.g.
https://www.smashingmagazine.com/2015/01/designing-for-print-with-css/#left-a...

Though I haven't actually tried this and I don't know how well we actually
support it.

[jzfeng, 2017/04/06 09:01:51]

I feel it is ok to leave as is?

For the normal case, the size of printed_pages is always one, so the code won't
change anything. These two thing can still be different for each page.

For the headless case, the page size and content area is not used by the print
manager. So I guess it won't matter.

[Lei Zhang, 2017/04/06 10:23:00]

That assumes nobody else will try to use UseSingleMetafile(). Since we can't
always predict the future, and this is a subtle difference that most readers
won't notice by just glancing at the code, can we leave a comment here to
describe the potential bug?

[jzfeng, 2017/04/07 03:24:06]

Done. Added this potential bug to the comment of the UseSingleMetafile method.

-  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();
+  }
 }
 
 #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