Retain ref-count of a bound ref-counted object in //printing

|data| at PrintedDocument::DebugDumpData argument is a ref-counted type,
and an explicit lifetime management is needed on base::Bind.

This pattern of raw pointers to a ref-counted object should be checked
in base::Bind implementation, but it has failed to ban the pattern when
the pointee was const.

Bug: 737010
Change-Id: Icf0b08418e6fcda2b88c61db32c25d88703362cf
Reviewed-on: https://chromium-review.googlesource.com/551437
Commit-Queue: Lei Zhang <thestig@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>
Cr-Commit-Position: refs/heads/master@{#483076}

printing/printed_document.cc

@@ -239,9 +239,10 @@ void PrintedDocument::DebugDumpData(
     const base::FilePath::StringType& extension) {
   if (g_debug_dump_info.Get().empty())
     return;
-  base::PostTaskWithTraits(
-      FROM_HERE, {base::TaskPriority::BACKGROUND, base::MayBlock()},
-      base::BindOnce(&DebugDumpDataTask, name(), extension, data));
+  base::PostTaskWithTraits(FROM_HERE,
+                           {base::TaskPriority::BACKGROUND, base::MayBlock()},
+                           base::BindOnce(&DebugDumpDataTask, name(), extension,
+                                          base::RetainedRef(data)));
 }
 
 PrintedDocument::Mutable::Mutable(PrintedPagesSource* source)