Printing API: Change printing.submitJob() documentation

Display the difference in behavior of printing.submitJob() for
extensions listed in PrintingAPIExtensionsWhitelist policy.

Bug: 996785
Change-Id: I197b2fd386fad90c731b50f995ce463a5ade6beb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2062411
Commit-Queue: Nikita Podguzov <nikitapodguzov@chromium.org>
Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#743469}

chrome/common/extensions/api/printing.idl

@@ -151,6 +151,8 @@ namespace printing {
 
   interface Functions {
     // Submits the job for print.
+    // If the extension is not listed in PrintingAPIExtensionsWhitelist policy,
+    // the user will be prompted to accept the print job.
     static void submitJob(SubmitJobRequest request, SubmitJobCallback callback);
 
     // Cancels previously submitted job.