Add error handling and unit test for pdf compositor service

components/printing/service/public/cpp/pdf_compositor_client.cc

 // Copyright 2017 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.
 
 #include "components/printing/service/public/cpp/pdf_compositor_client.h"
 
 #include <utility>
 
 #include "mojo/public/cpp/system/platform_handle.h"
 
 namespace printing {
 
 namespace {
 
 // Helper callback which owns an PdfCompositorPtr until invoked. This keeps the
 // PdfCompositor pipe open just long enough to dispatch a reply, at which point
 // the reply is forwarded to the wrapped |callback|.
 void OnCompositePdf(
     printing::mojom::PdfCompositorPtr compositor,
     printing::mojom::PdfCompositor::CompositePdfCallback callback,
     scoped_refptr<base::SequencedTaskRunner> task_runner,
+    mojom::PdfCompositor::Status status,
     mojo::ScopedSharedBufferHandle pdf_handle) {
-  task_runner->PostTask(FROM_HERE, base::BindOnce(std::move(callback),
+  task_runner->PostTask(FROM_HERE, base::BindOnce(std::move(callback), status,
                                                   base::Passed(&pdf_handle)));
 }
 
 }  // namespace
 
 PdfCompositorClient::PdfCompositorClient() : compositor_(nullptr) {}
 
 PdfCompositorClient::~PdfCompositorClient() {}
 
 void PdfCompositorClient::Connect(service_manager::Connector* connector) {
@@ skipping 15 matching lines @@
   mojo::ScopedSharedBufferHandle buffer_handle =
       mojo::WrapSharedMemoryHandle(handle, data_size, true);
 
   compositor_->CompositePdf(
       std::move(buffer_handle),
       base::BindOnce(&OnCompositePdf, base::Passed(&compositor_),
                      std::move(callback), callback_task_runner));
 }
 
 }  // namespace printing