Add error handling and unit test for pdf compositor service

components/printing/service/pdf_compositor_service.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/pdf_compositor_service.h"
 
 #include <utility>
 
 #include "base/lazy_instance.h"
 #include "base/memory/discardable_memory.h"
@@ skipping 25 matching lines @@
     : creator_(creator.empty() ? "Chromium" : creator), weak_factory_(this) {}
 
 PdfCompositorService::~PdfCompositorService() = default;
 
 // static
 std::unique_ptr<service_manager::Service> PdfCompositorService::Create(
     const std::string& creator) {
   return base::MakeUnique<printing::PdfCompositorService>(creator);
 }
 
-void PdfCompositorService::OnStart() {
+void PdfCompositorService::PrepareToStart() {
   // Set up discardable memory manager.
   discardable_memory::mojom::DiscardableSharedMemoryManagerPtr manager_ptr;
   context()->connector()->BindInterface(content::mojom::kBrowserServiceName,
                                         &manager_ptr);
   discardable_shared_memory_manager_ = base::MakeUnique<
       discardable_memory::ClientDiscardableSharedMemoryManager>(
       std::move(manager_ptr), content::UtilityThread::Get()->GetIOTaskRunner());
   DCHECK(discardable_shared_memory_manager_);
   base::DiscardableMemoryAllocator::SetInstance(
       discardable_shared_memory_manager_.get());
+}
+
+void PdfCompositorService::OnStart() {
+  PrepareToStart();
 
   ref_factory_ = base::MakeUnique<service_manager::ServiceContextRefFactory>(
       base::Bind(&service_manager::ServiceContext::RequestQuit,
                  base::Unretained(context())));
   registry_.AddInterface(
       base::Bind(&OnPdfCompositorRequest, creator_, ref_factory_.get()));
 }
 
 void PdfCompositorService::OnBindInterface(
     const service_manager::BindSourceInfo& source_info,
     const std::string& interface_name,
     mojo::ScopedMessagePipeHandle interface_pipe) {
   registry_.BindInterface(source_info, interface_name,
                           std::move(interface_pipe));
 }
 
 }  // namespace printing