Migrate //printing to OnceCallback

This updates //printing to use base::OnceCallback instead of legacy
base::Callback. No intended functional change is included.

This reduces the number of 'base::Bind' in //printing from 2 to 0 as
tracked at http://goo.gl/LUVhDj

Bug: 714018
Change-Id: Ic5ba394447c20b444d238511473bbfc7abbc9669
Reviewed-on: https://chromium-review.googlesource.com/954883Reviewed-by: Lei Zhang <thestig@chromium.org>
Commit-Queue: Taiju Tsuiki <tzik@chromium.org>
Cr-Commit-Position: refs/heads/master@{#542071}

printing/printing_context_win.cc

@@ -217,7 +217,7 @@ PrintingContext::Result PrintingContextWin::UpdatePrinterSettings(
   if (show_system_dialog) {
     PrintingContext::Result result = PrintingContext::FAILED;
     AskUserForSettings(page_count, false, false,
-                       base::Bind(&AssignResult, &result));
+                       base::BindOnce(&AssignResult, &result));
     return result;
   }
   // Set printer then refresh printer settings.

printing/printing_context_win_unittest.cc

@@ -148,11 +148,9 @@ TEST_F(PrintingContextTest, PrintAll) {
 
   MockPrintingContextWin context(this);
   context.AskUserForSettings(
-      123,
-      false,
-      false,
-      base::Bind(&PrintingContextTest::PrintSettingsCallback,
-                 base::Unretained(this)));
+      123, false, false,
+      base::BindOnce(&PrintingContextTest::PrintSettingsCallback,
+                     base::Unretained(this)));
   EXPECT_EQ(PrintingContext::OK, result());
   PrintSettings settings = context.settings();
   EXPECT_EQ(0u, settings.ranges().size());