Instead of ArrayBuffer, pass blob with printerProvider.onPrintRequested

extensions/common/api/printer_provider_internal.idl

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // printerProviderInternal
 // Internal API used to run callbacks passed to chrome.printerProvider API
 // events.
 // When dispatching a chrome.printerProvider API event, its arguments will be
 // massaged in custom bindings so a callback is added. The callback uses
 // chrome.printerProviderInternal API to report the event results.
 // In order to identify the event for which the callback is called, the event
 // is internally dispatched having a requestId argument (which is removed from
 // the argument list before the event actually reaches the event listeners). The
 // requestId is forwarded to the chrome.printerProviderInternal API functions.
 namespace printerProviderInternal {
   // Same as in printerProvider.PrintError enum API.
   enum PrintError { OK, FAILED, INVALID_TICKET, INVALID_DATA };
 
+  // Information needed by a renderer to create a blob instance.
+  dictionary BlobInfo {
+    // The blob UUID.
+    DOMString blobUuid;
+
+    // The blob content type.
+    DOMString type;
+
+    // The blob size.
+    long size;

[not at google - send to devlin, 2015/03/04 21:54:49]

Wow, big print job :-)

+  };
+
+  // Callback carrying information needed by a renderer to create a blob.
+  callback BlobCallback = void(BlobInfo blobInfo);
+
   interface Functions {
     // Runs callback to printerProvider.onGetPrintersRequested event.
     // |requestId|: Parameter identifying the event instance for which the
     //     callback is run.
     // |printers|: List of printers reported by the extension.
     void reportPrinters(long requestId,
                         optional printerProvider.PrinterInfo[] printers);
 
     // Runs callback to printerProvider.onGetCapabilityRequested event.
     // |requestId|: Parameter identifying the event instance for which the
     //     callback is run.
     // |error|: The printer capability returned by the extension.
     void reportPrinterCapability(long request_id, optional object capability);
 
     // Runs callback to printerProvider.onPrintRequested event.
     // |requestId|: Parameter identifying the event instance for which the
     //     callback is run.
     // |error|: The requested print job result.
     void reportPrintResult(long request_id, optional PrintError error);
+
+    // Gets information needed to create a print data blob for a print request.
+    // The blob will be dispatched to the extension via
+    // printerProvider.onPrintRequested event.
+    // |requestId|: The request id for the print request for which data is
+    //     needed.
+    // |callback|: Callback called with the information needed to create a blob
+    //     of print data.
+    void getPrintData(long requestId, BlobCallback callback);
   };
 };