Code:  PrintPreviewMessageHandler::PrintPreviewMessageHandler(
     WebContents* web_contents)
    : content::WebContentsObserver(web_contents) {
   DCHECK(web_contents);
 }

Commit Message: Use pdf compositor service for printing when OOPIF is enabled

When OOPIF is enabled (by site-per-process flag or
top-document-isolation feature), use the pdf compositor service for
converting PaintRecord to PDF on renderers.

In the future, this will make compositing PDF from multiple renderers
possible.

TBR=jzfeng@chromium.org
BUG=455764

Change-Id: I3c28f03f4358e4228239fe1a33384f85e7716e8f
Reviewed-on: https://chromium-review.googlesource.com/699765
Commit-Queue: Wei Li <weili@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>
Cr-Commit-Position: refs/heads/master@{#511616}
CWE ID: CWE-254
 PrintPreviewMessageHandler::PrintPreviewMessageHandler(
     WebContents* web_contents)
    : content::WebContentsObserver(web_contents), weak_ptr_factory_(this) {
   DCHECK(web_contents);
 }
