Print selections with print media.

PrepareFrameAndViewForPrint::CopySelection() generates HTML + CSS to
support printing only the selection. By making it do the generation in
print mode, the generated output will have print media CSS applied.

BUG=889226

Change-Id: Ia57d4c0429b93d72cb412545eda7579b53570e6c
Reviewed-on: https://chromium-review.googlesource.com/c/1308604Reviewed-by: Rebekah Potter <rbpotter@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
Cr-Commit-Position: refs/heads/master@{#607118}

components/printing/renderer/print_render_frame_helper.cc

@@ -827,7 +827,7 @@ PrepareFrameAndViewForPrint::PrepareFrameAndViewForPrint(
       weak_ptr_factory_(this) {
   PrintMsg_Print_Params print_params = params;
   bool source_is_pdf = PrintingNodeOrPdfFrame(frame, node_to_print_);
-  if (!should_print_selection_only_ || !source_is_pdf) {
+  if (!should_print_selection_only_) {
     bool fit_to_page =
         ignore_css_margins && IsWebPrintScalingOptionFitToPage(print_params);
     ComputeWebKitPrintParamsInDesiredDpi(params, source_is_pdf,
@@ -906,8 +906,11 @@ void PrepareFrameAndViewForPrint::CopySelectionIfNeeded(
 void PrepareFrameAndViewForPrint::CopySelection(
     const WebPreferences& preferences) {
   ResizeForPrinting();
+  frame()->PrintBegin(web_print_params_, node_to_print_);
   std::string html = frame()->SelectionAsMarkup().Utf8();
+  frame()->PrintEnd();
   RestoreSize();
+
   // Create a new WebView with the same settings as the current display one.
   // Except that we disable javascript (don't want any active content running
   // on the page).