Tweak the print APIs.

1. Adding bundle with metadata to PrintDocumentAdapter#onLayout
   with one key for now to specify whether this is for a preview.

2. Cleaned up docs.

Change-Id: I89380781bf3ae41aa89f8a0347d74516a210394c
diff --git a/packages/PrintSpooler/src/com/android/printspooler/PrintJobConfigActivity.java b/packages/PrintSpooler/src/com/android/printspooler/PrintJobConfigActivity.java
index 659102c..c0faed8 100644
--- a/packages/PrintSpooler/src/com/android/printspooler/PrintJobConfigActivity.java
+++ b/packages/PrintSpooler/src/com/android/printspooler/PrintJobConfigActivity.java
@@ -536,6 +536,7 @@
         // TODO: Implement old attributes tracking
         mPrintSpooler.setPrintJobAttributes(mPrintJobId, mPrintAttributes);
 
+        // TODO: Implement setting the print preview attribute
         mRemotePrintAdapter.layout(new PrintAttributes.Builder().create(),
                 mPrintAttributes, new LayoutResultCallback() {
             @Override
@@ -566,7 +567,7 @@
                 Log.e(LOG_TAG, "Error during layout: " + error);
                 finishActivity(Activity.RESULT_CANCELED);
             }
-        });
+        }, new Bundle());
     }
 
     private void notifyPrintableFinishIfNeeded() {