Create a refcounted usb context wrapper.

This will be also used when we introduce UsbDevice.

BUG=223817

Review URL: https://chromiumcodereview.appspot.com/20012002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@215174 0039d316-1c4b-4281-b951-d872f2087c98

10 files changed, 326 insertions, 121 deletions

diff --git a/chrome/browser/devtools/adb/android_usb_device.cc b/chrome/browser/devtools/adb/android_usb_device.cc
index 36965ed..c6f537c 100644
--- a/chrome/browser/devtools/adb/android_usb_device.cc
+++ b/chrome/browser/devtools/adb/android_usb_device.cc
@@ -149,11 +149,11 @@ static void RespondOnUIThread(const AndroidUsbDevicesCallback& callback,
   callback.Run(devices);
 }
 
-static void EnumerateOnFileThread(UsbService* service,
-                                  crypto::RSAPrivateKey* rsa_key,
+static void EnumerateOnFileThread(crypto::RSAPrivateKey* rsa_key,
                                   const AndroidUsbDevicesCallback& callback) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
 
+  UsbService* service = UsbService::GetInstance();
   AndroidUsbDevices& devices = g_devices.Get();
 
   UsbDevices usb_devices;
@@ -207,10 +207,9 @@ static void EnumerateOnFileThread(UsbService* service,
 void AndroidUsbDevice::Enumerate(crypto::RSAPrivateKey* rsa_key,
                                  const AndroidUsbDevicesCallback& callback) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
-  UsbService* service = UsbService::GetInstance();
   BrowserThread::PostTask(
       BrowserThread::FILE, FROM_HERE,
-      base::Bind(&EnumerateOnFileThread, service, rsa_key, callback));
+      base::Bind(&EnumerateOnFileThread, rsa_key, callback));
 }
 
 AndroidUsbDevice::AndroidUsbDevice(crypto::RSAPrivateKey* rsa_key,
diff --git a/chrome/browser/extensions/api/usb/usb_api.cc b/chrome/browser/extensions/api/usb/usb_api.cc
index 223f831..a6c8ae8 100644
--- a/chrome/browser/extensions/api/usb/usb_api.cc
+++ b/chrome/browser/extensions/api/usb/usb_api.cc
@@ -326,6 +326,14 @@ static base::Value* PopulateInterfaceDescriptor(int interface_number,
   return descriptor.ToValue().release();
 }
 
+void GetUsbService(base::Callback<void(UsbService* service)> callback) {
+  BrowserThread::PostTaskAndReplyWithResult(
+      BrowserThread::FILE,
+      FROM_HERE,
+      base::Bind(UsbService::GetInstance),
+      callback);
+}
+
 }  // namespace
 
 namespace extensions {
@@ -440,21 +448,48 @@ void UsbFindDevicesFunction::AsyncWorkStart() {
     return;
   }
 
-  UsbService::GetInstance()->FindDevices(
-      vendor_id,
-      product_id,
-      interface_id,
-      &devices_,
-      base::Bind(&UsbFindDevicesFunction::OnCompleted, this));
+  GetUsbService(base::Bind(&UsbFindDevicesFunction::EnumerateDevices,
+                           this,
+                           vendor_id,
+                           product_id,
+                           interface_id));
+}
+
+void UsbFindDevicesFunction::EnumerateDevices(
+    uint16_t vendor_id,
+    uint16_t product_id,
+    int interface_id,
+    UsbService* service) {
+  BrowserThread::PostTask(
+      BrowserThread::FILE,
+      FROM_HERE,
+      base::Bind(&UsbService::FindDevices,
+                 base::Unretained(service),
+                 vendor_id,
+                 product_id,
+                 interface_id,
+                 base::Bind(&UsbFindDevicesFunction::OnEnumerationCompleted,
+                            this)));
+}
+
+
+void UsbFindDevicesFunction::OnEnumerationCompleted(
+    ScopedDeviceVector devices) {
+  BrowserThread::PostTask(
+      BrowserThread::IO,
+      FROM_HERE,
+      base::Bind(&UsbFindDevicesFunction::OnCompleted,
+                 this,
+                 base::Passed(devices.Pass())));
 }
 
-void UsbFindDevicesFunction::OnCompleted() {
-  for (size_t i = 0; i < devices_.size(); ++i) {
-    UsbDeviceHandle* const device = devices_[i].get();
+void UsbFindDevicesFunction::OnCompleted(
+    ScopedDeviceVector devices) {
+  for (size_t i = 0; i < devices->size(); ++i) {
+    UsbDeviceHandle* const device = devices->at(i).get();
     UsbDeviceResource* const resource =
         new UsbDeviceResource(extension_->id(), device);
 
-    Device js_device;
     result_->Append(PopulateDevice(manager_->Add(resource),
                                    parameters_->options.vendor_id,
                                    parameters_->options.product_id));
diff --git a/chrome/browser/extensions/api/usb/usb_api.h b/chrome/browser/extensions/api/usb/usb_api.h
index 80941fc..65c713e 100644
--- a/chrome/browser/extensions/api/usb/usb_api.h
+++ b/chrome/browser/extensions/api/usb/usb_api.h
@@ -16,6 +16,7 @@
 #include "net/base/io_buffer.h"
 
 class UsbDeviceHandle;
+class UsbService;
 
 namespace extensions {
 
@@ -71,10 +72,21 @@ class UsbFindDevicesFunction : public UsbAsyncApiFunction {
   virtual void AsyncWorkStart() OVERRIDE;
 
  private:
-  void OnCompleted();
+  typedef scoped_ptr<std::vector<scoped_refptr<UsbDeviceHandle> > >
+      ScopedDeviceVector;
+
+  // Wait for GetDeviceService to return and start enumeration on FILE thread.
+  void EnumerateDevices(uint16_t vendor_id,
+                        uint16_t product_id,
+                        int interface_id,
+                        UsbService* service);
+  // Relay the result on IO thread to OnCompleted.
+  void OnEnumerationCompleted(ScopedDeviceVector devices);
+
+  // Create ApiResources and reply.
+  void OnCompleted(ScopedDeviceVector devices);
 
   scoped_ptr<base::ListValue> result_;
-  std::vector<scoped_refptr<UsbDeviceHandle> > devices_;
   scoped_ptr<extensions::api::usb::FindDevices::Params> parameters_;
 };
 
diff --git a/chrome/browser/usb/usb_context.cc b/chrome/browser/usb/usb_context.cc
new file mode 100644
index 0000000..3b0811a
--- /dev/null
+++ b/chrome/browser/usb/usb_context.cc
@@ -0,0 +1,73 @@
+// Copyright 2013 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 "chrome/browser/usb/usb_context.h"
+
+#include "base/logging.h"
+#include "base/synchronization/waitable_event.h"
+#include "base/threading/platform_thread.h"
+#include "content/public/browser/browser_thread.h"
+#include "third_party/libusb/src/libusb/interrupt.h"
+#include "third_party/libusb/src/libusb/libusb.h"
+
+// The UsbEventHandler works around a design flaw in the libusb interface. There
+// is currently no way to signal to libusb that any caller into one of the event
+// handler calls should return without handling any events.
+class UsbContext::UsbEventHandler : public base::PlatformThread::Delegate {
+ public:
+  explicit UsbEventHandler(libusb_context* context);
+  virtual ~UsbEventHandler();
+
+  // base::PlatformThread::Delegate
+  virtual void ThreadMain() OVERRIDE;
+
+ private:
+  volatile bool running_;
+  libusb_context* context_;
+  base::PlatformThreadHandle thread_handle_;
+  base::WaitableEvent start_polling_;
+  DISALLOW_COPY_AND_ASSIGN(UsbEventHandler);
+};
+
+UsbContext::UsbEventHandler::UsbEventHandler(libusb_context* context)
+    : running_(true),
+      context_(context),
+      thread_handle_(0),
+      start_polling_(false, false) {
+  DCHECK(base::PlatformThread::Create(0, this, &thread_handle_)) <<
+      "Failed to create USB IO handling thread.";
+  start_polling_.Wait();
+}
+
+UsbContext::UsbEventHandler::~UsbEventHandler() {
+  running_ = false;
+  // Spreading running_ to the UsbEventHandler thread.
+  base::subtle::MemoryBarrier();
+  libusb_interrupt_handle_event(context_);
+  base::PlatformThread::Join(thread_handle_);
+}
+
+void UsbContext::UsbEventHandler::ThreadMain() {
+  base::PlatformThread::SetName("UsbEventHandler");
+  VLOG(1) << "UsbEventHandler started.";
+  if (running_) {
+    start_polling_.Signal();
+    libusb_handle_events(context_);
+  }
+  while (running_)
+    libusb_handle_events(context_);
+  VLOG(1) << "UsbEventHandler shutting down.";
+}
+
+UsbContext::UsbContext() : context_(NULL) {
+  CHECK_EQ(0, libusb_init(&context_)) << "Cannot initialize libusb";
+  event_handler_.reset(new UsbEventHandler(context_));
+}
+
+UsbContext::~UsbContext() {
+  // destruction of UsbEventHandler is a blocking operation.
+  CHECK(content::BrowserThread::CurrentlyOn(content::BrowserThread::FILE));
+  event_handler_.reset(NULL);
+  libusb_exit(context_);
+}
diff --git a/chrome/browser/usb/usb_context.h b/chrome/browser/usb/usb_context.h
new file mode 100644
index 0000000..07894c5
--- /dev/null
+++ b/chrome/browser/usb/usb_context.h
@@ -0,0 +1,46 @@
+// Copyright 2013 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.
+
+#ifndef CHROME_BROWSER_USB_USB_CONTEXT_H_
+#define CHROME_BROWSER_USB_USB_CONTEXT_H_
+
+#include "base/basictypes.h"
+#include "base/memory/ref_counted.h"
+#include "base/memory/scoped_ptr.h"
+#include "content/public/browser/browser_thread.h"
+
+struct libusb_context;
+
+typedef libusb_context* PlatformUsbContext;
+
+// Ref-counted wrapper for libusb_context*.
+// It also manages the life-cycle of UsbEventHandler.
+// It is a blocking operation to delete UsbContext.
+// Destructor must be called on FILE thread.
+class UsbContext
+    : public base::RefCountedThreadSafe<
+          UsbContext, content::BrowserThread::DeleteOnFileThread> {
+ public:
+  PlatformUsbContext context() const { return context_; }
+
+ protected:
+  friend class UsbService;
+  friend struct content::BrowserThread::DeleteOnThread<
+      content::BrowserThread::FILE>;
+  friend class base::DeleteHelper<UsbContext>;
+
+  // Set wait_for_polling_starts to true if the constructor should wait until
+  // the polling starts. It will block the current thread. Only use it in tests.
+  explicit UsbContext();
+  virtual ~UsbContext();
+
+ private:
+  class UsbEventHandler;
+  PlatformUsbContext context_;
+  scoped_ptr<UsbEventHandler> event_handler_;
+
+  DISALLOW_COPY_AND_ASSIGN(UsbContext);
+};
+
+#endif  // CHROME_BROWSER_USB_USB_CONTEXT_H_
diff --git a/chrome/browser/usb/usb_service_unittest.cc b/chrome/browser/usb/usb_context_unittest.cc
index 44864d8..4944c1c 100644
--- a/chrome/browser/usb/usb_service_unittest.cc
+++ b/chrome/browser/usb/usb_context_unittest.cc
@@ -2,16 +2,23 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#include "chrome/browser/usb/usb_service.h"
+#include "chrome/browser/usb/usb_context.h"
 
+#include "base/threading/platform_thread.h"
 #include "build/build_config.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace {
 
-class UsbServiceTest : public testing::Test {
+class UsbContextTest : public testing::Test {
  protected:
-  class UsbServiceForTest : public UsbService {};
+  class UsbContextForTest : public UsbContext {
+   public:
+    UsbContextForTest() : UsbContext() {}
+   private:
+    virtual ~UsbContextForTest() {}
+    DISALLOW_COPY_AND_ASSIGN(UsbContextForTest);
+  };
 };
 
 #if defined(OS_LINUX)
@@ -24,10 +31,10 @@ class UsbServiceTest : public testing::Test {
 #define MAYBE_GracefulShutdown GracefulShutdown
 #endif
 
-TEST_F(UsbServiceTest, MAYBE_GracefulShutdown) {
+TEST_F(UsbContextTest, MAYBE_GracefulShutdown) {
   base::TimeTicks start = base::TimeTicks::Now();
   {
-    scoped_ptr<UsbServiceForTest> service(new UsbServiceForTest());
+    scoped_refptr<UsbContextForTest> context(new UsbContextForTest());
   }
   base::TimeDelta elapse = base::TimeTicks::Now() - start;
   if (elapse > base::TimeDelta::FromSeconds(2)) {
diff --git a/chrome/browser/usb/usb_device_handle.cc b/chrome/browser/usb/usb_device_handle.cc
index b6e54f4..56c3dc7 100644
--- a/chrome/browser/usb/usb_device_handle.cc
+++ b/chrome/browser/usb/usb_device_handle.cc
@@ -1,4 +1,4 @@
-// Copyright 2013 The Chromium Authors. All rights reserved.
+// Copyright (c) 2013 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.
 
@@ -127,7 +127,7 @@ void UsbDeviceHandle::TransferComplete(PlatformUsbTransferHandle handle) {
   DCHECK(ContainsKey(transfers_, handle)) << "Missing transfer completed";
   Transfer* const transfer = &transfers_[handle];
 
-  DCHECK(handle->actual_length >= 0) << "Negative actual length received";
+  DCHECK_GE(handle->actual_length, 0) << "Negative actual length received";
   size_t actual_length =
       static_cast<size_t>(std::max(handle->actual_length, 0));
 
@@ -272,9 +272,15 @@ bool UsbDeviceHandle::GetSerial(base::string16* serial) {
     size = libusb_get_string_descriptor(
         handle_, desc.iSerialNumber, langid[i],
         reinterpret_cast<unsigned char*>(&text[0]), sizeof(text));
-    if (size < 0)
+    if (size <= 2)
       continue;
-    *serial = base::string16(text, size / 2);
+    if ((text[0] >> 8) != LIBUSB_DT_STRING)
+      continue;
+    if ((text[0] & 255) > size)
+      continue;
+
+    size = size / 2 - 1;
+    *serial = base::string16(text + 1, size);
     return true;
   }
   return false;
diff --git a/chrome/browser/usb/usb_device_handle.h b/chrome/browser/usb/usb_device_handle.h
index ef059d7..0659955 100644
--- a/chrome/browser/usb/usb_device_handle.h
+++ b/chrome/browser/usb/usb_device_handle.h
@@ -1,4 +1,4 @@
-// Copyright 2013 The Chromium Authors. All rights reserved.
+// Copyright (c) 2013 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.
 
diff --git a/chrome/browser/usb/usb_service.cc b/chrome/browser/usb/usb_service.cc
index 9cba20cc..d850488 100644
--- a/chrome/browser/usb/usb_service.cc
+++ b/chrome/browser/usb/usb_service.cc
@@ -10,9 +10,13 @@
 #include "base/bind_helpers.h"
 #include "base/logging.h"
 #include "base/stl_util.h"
-#include "base/synchronization/waitable_event.h"
+#include "chrome/browser/chrome_notification_types.h"
+#include "chrome/browser/usb/usb_context.h"
 #include "chrome/browser/usb/usb_device_handle.h"
-#include "third_party/libusb/src/libusb/interrupt.h"
+#include "content/public/browser/browser_thread.h"
+#include "content/public/browser/notification_observer.h"
+#include "content/public/browser/notification_registrar.h"
+#include "content/public/browser/notification_service.h"
 #include "third_party/libusb/src/libusb/libusb.h"
 
 #if defined(OS_CHROMEOS)
@@ -21,70 +25,64 @@
 #include "chromeos/dbus/permission_broker_client.h"
 #endif  // defined(OS_CHROMEOS)
 
-using std::vector;
+namespace content {
 
-// The UsbEventHandler works around a design flaw in the libusb interface. There
-// is currently no way to signal to libusb that any caller into one of the event
-// handler calls should return without handling any events.
-class UsbEventHandler : public base::PlatformThread::Delegate {
- public:
-  explicit UsbEventHandler(PlatformUsbContext context)
-      : running_(true),
-        context_(context),
-        thread_handle_(0),
-        started_event_(false, false) {
-    base::PlatformThread::Create(0, this, &thread_handle_);
-    started_event_.Wait();
-  }
+class NotificationDetails;
+class NotificationSource;
 
-  virtual ~UsbEventHandler() {}
+}  // namespace content
 
-  virtual void ThreadMain() OVERRIDE {
-    base::PlatformThread::SetName("UsbEventHandler");
-    VLOG(1) << "UsbEventHandler started.";
-    started_event_.Signal();
-    while (running_)
-      libusb_handle_events(context_);
-    VLOG(1) << "UsbEventHandler shutting down.";
-  }
+using content::BrowserThread;
+using std::vector;
+
+namespace {
 
-  void Stop() {
-    running_ = false;
-    base::subtle::MemoryBarrier();
-    libusb_interrupt_handle_event(context_);
-    base::PlatformThread::Join(thread_handle_);
+class ExitObserver : public content::NotificationObserver {
+ public:
+  explicit ExitObserver(UsbService* service) : service_(service) {
+    registrar_.Add(this, chrome::NOTIFICATION_APP_TERMINATING,
+                   content::NotificationService::AllSources());
   }
 
  private:
-  volatile bool running_;
-  PlatformUsbContext context_;
-  base::PlatformThreadHandle thread_handle_;
-  base::WaitableEvent started_event_;
-  DISALLOW_COPY_AND_ASSIGN(UsbEventHandler);
+  // content::NotificationObserver
+  virtual void Observe(int type,
+                       const content::NotificationSource& source,
+                       const content::NotificationDetails& details) OVERRIDE {
+    if (type == chrome::NOTIFICATION_APP_TERMINATING) {
+      registrar_.RemoveAll();
+      BrowserThread::DeleteSoon(BrowserThread::FILE, FROM_HERE, service_);
+    }
+  }
+  UsbService* service_;
+  content::NotificationRegistrar registrar_;
 };
 
-UsbService::UsbService() {
-  libusb_init(&context_);
-  event_handler_ = new UsbEventHandler(context_);
+}  // namespace
+
+UsbService::UsbService() : context_(new UsbContext()) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
 }
 
 UsbService::~UsbService() {
-  event_handler_->Stop();
-  delete event_handler_;
-  libusb_exit(context_);
-  context_ = NULL;
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
+  // UsbDeviceHandle::Close removes itself from devices_.
+  while (devices_.size())
+    devices_.begin()->second->Close();
 }
 
 UsbService* UsbService::GetInstance() {
-  return Singleton<UsbService>::get();
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
+  // UsbService deletes itself upon APP_TERMINATING.
+  return Singleton<UsbService, LeakySingletonTraits<UsbService> >::get();
 }
 
-void UsbService::FindDevices(const uint16 vendor_id,
-                             const uint16 product_id,
-                             int interface_id,
-                             vector<scoped_refptr<UsbDeviceHandle> >* devices,
-                             const base::Callback<void()>& callback) {
-  DCHECK(event_handler_) << "FindDevices called after event handler stopped.";
+void UsbService::FindDevices(
+    const uint16 vendor_id,
+    const uint16 product_id,
+    int interface_id,
+    const base::Callback<void(ScopedDeviceVector vector)>& callback) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
 #if defined(OS_CHROMEOS)
   // ChromeOS builds on non-ChromeOS machines (dev) should not attempt to
   // use permission broker.
@@ -93,29 +91,33 @@ void UsbService::FindDevices(const uint16 vendor_id,
         chromeos::DBusThreadManager::Get()->GetPermissionBrokerClient();
     DCHECK(client) << "Could not get permission broker client.";
     if (!client) {
-      callback.Run();
+      callback.Run(ScopedDeviceVector());
       return;
     }
 
-    client->RequestUsbAccess(vendor_id,
-                             product_id,
-                             interface_id,
-                             base::Bind(&UsbService::FindDevicesImpl,
-                                        base::Unretained(this),
-                                        vendor_id,
-                                        product_id,
-                                        devices,
-                                        callback));
+    BrowserThread::PostTask(
+        BrowserThread::UI,
+        FROM_HERE,
+        base::Bind(&chromeos::PermissionBrokerClient::RequestUsbAccess,
+                   base::Unretained(client),
+                   vendor_id,
+                   product_id,
+                   interface_id,
+                   base::Bind(&UsbService::OnRequestUsbAccessReplied,
+                              base::Unretained(this),
+                              vendor_id,
+                              product_id,
+                              callback)));
   } else {
-    FindDevicesImpl(vendor_id, product_id, devices, callback, true);
+    FindDevicesImpl(vendor_id, product_id, callback, true);
   }
 #else
-  FindDevicesImpl(vendor_id, product_id, devices, callback, true);
+  FindDevicesImpl(vendor_id, product_id, callback, true);
 #endif  // defined(OS_CHROMEOS)
 }
 
 void UsbService::EnumerateDevices(
-    std::vector<scoped_refptr<UsbDeviceHandle> >* devices) {
+    vector<scoped_refptr<UsbDeviceHandle> >* devices) {
   devices->clear();
 
   DeviceVector enumerated_devices;
@@ -130,21 +132,36 @@ void UsbService::EnumerateDevices(
   }
 }
 
-void UsbService::FindDevicesImpl(
+void UsbService::OnRequestUsbAccessReplied(
     const uint16 vendor_id,
     const uint16 product_id,
-    vector<scoped_refptr<UsbDeviceHandle> >* devices,
-    const base::Callback<void()>& callback,
+    const base::Callback<void(ScopedDeviceVector vectors)>& callback,
     bool success) {
-  base::ScopedClosureRunner run_callback(callback);
+  BrowserThread::PostTask(
+      BrowserThread::FILE,
+      FROM_HERE,
+      base::Bind(&UsbService::FindDevicesImpl,
+                 base::Unretained(this),
+                 vendor_id,
+                 product_id,
+                 callback,
+                 success));
+}
 
-  devices->clear();
+void UsbService::FindDevicesImpl(
+    const uint16 vendor_id,
+    const uint16 product_id,
+    const base::Callback<void(ScopedDeviceVector vectors)>& callback,
+    bool success) {
+  ScopedDeviceVector devices(new vector<scoped_refptr<UsbDeviceHandle> >());
 
   // If the permission broker was unable to obtain permission for the specified
   // devices then there is no point in attempting to enumerate the devices. On
   // platforms without a permission broker, we assume permission is granted.
-  if (!success)
+  if (!success) {
+    callback.Run(devices.Pass());
     return;
+  }
 
   DeviceVector enumerated_devices;
   EnumerateDevicesImpl(&enumerated_devices);
@@ -155,14 +172,13 @@ void UsbService::FindDevicesImpl(
     if (DeviceMatches(device, vendor_id, product_id)) {
       UsbDeviceHandle* const wrapper = LookupOrCreateDevice(device);
       if (wrapper)
-        devices->push_back(wrapper);
+        devices->push_back(make_scoped_refptr(wrapper));
     }
   }
+  callback.Run(devices.Pass());
 }
 
 void UsbService::CloseDevice(scoped_refptr<UsbDeviceHandle> device) {
-  DCHECK(event_handler_) << "CloseDevice called after event handler stopped.";
-
   PlatformUsbDevice platform_device = libusb_get_device(device->handle());
   if (!ContainsKey(devices_, platform_device)) {
     LOG(WARNING) << "CloseDevice called for device we're not tracking!";
@@ -195,7 +211,9 @@ void UsbService::EnumerateDevicesImpl(DeviceVector* output) {
   STLClearObject(output);
 
   libusb_device** devices = NULL;
-  const ssize_t device_count = libusb_get_device_list(context_, &devices);
+  const ssize_t device_count = libusb_get_device_list(
+      context_->context(),
+      &devices);
   if (device_count < 0)
     return;
 
diff --git a/chrome/browser/usb/usb_service.h b/chrome/browser/usb/usb_service.h
index 5588364..dcd6e28 100644
--- a/chrome/browser/usb/usb_service.h
+++ b/chrome/browser/usb/usb_service.h
@@ -11,15 +11,16 @@
 
 #include "base/basictypes.h"
 #include "base/memory/singleton.h"
-#include "base/threading/platform_thread.h"
 #include "chrome/browser/usb/usb_device_handle.h"
-#include "third_party/libusb/src/libusb/libusb.h"
 
-class UsbEventHandler;
-template <typename T> struct DefaultSingletonTraits;
-struct libusb_context;
+namespace base {
+
+template <class T> class DeleteHelper;
 
-typedef struct libusb_context* PlatformUsbContext;
+}  // namespace base
+
+template <typename T> struct DefaultSingletonTraits;
+class UsbContext;
 
 // The USB service handles creating and managing an event handler thread that is
 // used to manage and dispatch USB events. It is also responsbile for device
@@ -27,16 +28,19 @@ typedef struct libusb_context* PlatformUsbContext;
 // competition for the same USB device.
 class UsbService {
  public:
+  typedef scoped_ptr<std::vector<scoped_refptr<UsbDeviceHandle> > >
+      ScopedDeviceVector;
+  // Must be called on FILE thread.
   static UsbService* GetInstance();
 
   // Find all of the devices attached to the system that are identified by
   // |vendor_id| and |product_id|, inserting them into |devices|. Clears
   // |devices| before use. Calls |callback| once |devices| is populated.
-  void FindDevices(const uint16 vendor_id,
-                   const uint16 product_id,
-                   int interface_id,
-                   std::vector<scoped_refptr<UsbDeviceHandle> >* devices,
-                   const base::Callback<void()>& callback);
+  void FindDevices(
+      const uint16 vendor_id,
+      const uint16 product_id,
+      int interface_id,
+      const base::Callback<void(ScopedDeviceVector vector)>& callback);
 
   // Find all of the devices attached to the system, inserting them into
   // |devices|. Clears |devices| before use.
@@ -46,13 +50,11 @@ class UsbService {
   // UsbDevice's Close function and disposes of the associated platform handle.
   void CloseDevice(scoped_refptr<UsbDeviceHandle> device);
 
- protected:
+ private:
   UsbService();
   virtual ~UsbService();
-
- private:
   friend struct DefaultSingletonTraits<UsbService>;
-
+  friend class base::DeleteHelper<UsbService>;
 
   // RefCountedPlatformUsbDevice takes care of managing the underlying reference
   // count of a single PlatformUsbDevice. This allows us to construct things
@@ -77,15 +79,23 @@ class UsbService {
                             const uint16 vendor_id,
                             const uint16 product_id);
 
+  // This method is called when permission broker replied our request.
+  // We will simply relay it to FILE thread.
+  void OnRequestUsbAccessReplied(
+      const uint16 vendor_id,
+      const uint16 product_id,
+      const base::Callback<void(ScopedDeviceVector vector)>& callback,
+      bool success);
+
   // FindDevicesImpl is called by FindDevices on ChromeOS after the permission
-  // broker has signalled that permission has been granted to access the
+  // broker has signaled that permission has been granted to access the
   // underlying device nodes. On other platforms, it is called directly by
   // FindDevices.
-  void FindDevicesImpl(const uint16 vendor_id,
-                       const uint16 product_id,
-                       std::vector<scoped_refptr<UsbDeviceHandle> >* devices,
-                       const base::Callback<void()>& callback,
-                       bool success);
+  void FindDevicesImpl(
+      const uint16 vendor_id,
+      const uint16 product_id,
+      const base::Callback<void(ScopedDeviceVector vector)>& callback,
+      bool success);
 
   // Populates |output| with the result of enumerating all attached USB devices.
   void EnumerateDevicesImpl(DeviceVector* output);
@@ -95,8 +105,7 @@ class UsbService {
   // the wrapper with the device internally.
   UsbDeviceHandle* LookupOrCreateDevice(PlatformUsbDevice device);
 
-  PlatformUsbContext context_;
-  UsbEventHandler* event_handler_;
+  scoped_refptr<UsbContext> context_;
 
   // The devices_ map contains scoped_refptrs to all open devices, indicated by
   // their vendor and product id. This allows for reusing an open device without