Web MIDI: make platform dependent initialization asynchronous

Since Android port needs asynchronous initialization, MIDIManager
should provide asynchronous initialization scheme for platform
dependent initialization.

BUG=339746
TEST=out/Debug/media_unittests --gtest_filter='Midi*.*'

Review URL: https://codereview.chromium.org/253493008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@267555 0039d316-1c4b-4281-b951-d872f2087c98

13 files changed, 348 insertions, 102 deletions

diff --git a/media/media.gyp b/media/media.gyp
index 3e215b1..557ebaa 100644
--- a/media/media.gyp
+++ b/media/media.gyp
@@ -1053,6 +1053,7 @@
         'filters/video_frame_scheduler_unittest.cc',
         'filters/video_frame_stream_unittest.cc',
         'filters/video_renderer_impl_unittest.cc',
+        'midi/midi_manager_unittest.cc',
         'midi/midi_manager_usb_unittest.cc',
         'midi/midi_message_queue_unittest.cc',
         'midi/midi_message_util_unittest.cc',
diff --git a/media/midi/midi_manager.cc b/media/midi/midi_manager.cc
index 7384703..67845ce 100644
--- a/media/midi/midi_manager.cc
+++ b/media/midi/midi_manager.cc
@@ -4,8 +4,6 @@
 
 #include "media/midi/midi_manager.h"
 
-#include "base/bind.h"
-#include "base/bind_helpers.h"
 #include "base/debug/trace_event.h"
 
 namespace media {
@@ -26,18 +24,41 @@ MidiManager::~MidiManager() {
 }
 
 void MidiManager::StartSession(MidiManagerClient* client, int client_id) {
+  bool session_is_ready;
+  bool session_needs_initialization = false;
+
+  {
+    base::AutoLock auto_lock(clients_lock_);
+    session_is_ready = initialized_;
+    if (!session_is_ready) {
+      // Call StartInitialization() only for the first request.
+      session_needs_initialization = pending_clients_.empty();
+      pending_clients_.insert(
+          std::pair<int, MidiManagerClient*>(client_id, client));
+    }
+  }
+
   // Lazily initialize the MIDI back-end.
-  if (!initialized_) {
-    initialized_ = true;
-    result_ = Initialize();
+  if (!session_is_ready) {
+    if (session_needs_initialization) {
+      TRACE_EVENT0("midi", "MidiManager::StartInitialization");
+      StartInitialization();
+    }
+    // CompleteInitialization() will be called asynchronously when platform
+    // dependent initialization is finished.
+    return;
   }
 
-  if (result_ == MIDI_OK) {
+  // Platform dependent initialization was already finished for previously
+  // initialized clients.
+  MidiResult result;
+  {
     base::AutoLock auto_lock(clients_lock_);
-    clients_.insert(client);
+    if (result_ == MIDI_OK)
+      clients_.insert(client);
+    result = result_;
   }
-  // TODO(toyoshim): Make Initialize() asynchronous.
-  client->CompleteStartSession(client_id, result_);
+  client->CompleteStartSession(client_id, result);
 }
 
 void MidiManager::EndSession(MidiManagerClient* client) {
@@ -54,9 +75,28 @@ void MidiManager::DispatchSendMidiData(MidiManagerClient* client,
   NOTREACHED();
 }
 
-MidiResult MidiManager::Initialize() {
-  TRACE_EVENT0("midi", "MidiManager::Initialize");
-  return MIDI_NOT_SUPPORTED;
+void MidiManager::StartInitialization() {
+  CompleteInitialization(MIDI_NOT_SUPPORTED);
+}
+
+void MidiManager::CompleteInitialization(MidiResult result) {
+  TRACE_EVENT0("midi", "MidiManager::CompleteInitialization");
+
+  base::AutoLock auto_lock(clients_lock_);
+  DCHECK(clients_.empty());
+  DCHECK(!pending_clients_.empty());
+  DCHECK(!initialized_);
+  initialized_ = true;
+  result_ = result;
+
+  for (PendingClientMap::iterator it = pending_clients_.begin();
+       it != pending_clients_.end();
+       ++it) {
+    if (result_ == MIDI_OK)
+      clients_.insert(it->second);
+    it->second->CompleteStartSession(it->first, result_);
+  }
+  pending_clients_.clear();
 }
 
 void MidiManager::AddInputPort(const MidiPortInfo& info) {
diff --git a/media/midi/midi_manager.h b/media/midi/midi_manager.h
index c21c66a..156a246 100644
--- a/media/midi/midi_manager.h
+++ b/media/midi/midi_manager.h
@@ -5,6 +5,7 @@
 #ifndef MEDIA_MIDI_MIDI_MANAGER_H_
 #define MEDIA_MIDI_MIDI_MANAGER_H_
 
+#include <map>
 #include <set>
 #include <vector>
 
@@ -89,9 +90,19 @@ class MEDIA_EXPORT MidiManager {
   const MidiPortInfoList& output_ports() { return output_ports_; }
 
  protected:
-  // Initializes the MIDI system, returning |true| on success.
-  // The default implementation is for unsupported platforms.
-  virtual MidiResult Initialize();
+  friend class MidiManagerUsb;
+
+  // Initializes the platform dependent MIDI system. It will call
+  // CompleteInitialization() asynchronously when initialization is finished.
+  // |result| of CompleteInitialization() will be MIDI_OK on success.
+  // MidiManager has a default implementation that calls
+  // CompleteInitialization() with MIDI_NOT_SUPPORTED.
+  virtual void StartInitialization();
+
+  // Called from a platform dependent implementation of StartInitialization().
+  // It will distribute |result| to MIDIManagerClient objects in
+  // |pending_clients_|.
+  void CompleteInitialization(MidiResult result);
 
   void AddInputPort(const MidiPortInfo& info);
   void AddOutputPort(const MidiPortInfo& info);
@@ -119,7 +130,11 @@ class MEDIA_EXPORT MidiManager {
   typedef std::set<MidiManagerClient*> ClientList;
   ClientList clients_;
 
-  // Protects access to our clients.
+  // Keeps track of all clients who are waiting for CompleteStartSession().
+  typedef std::map<int, MidiManagerClient*> PendingClientMap;
+  PendingClientMap pending_clients_;
+
+  // Protects access to our clients, |clients_| and |pending_clients_|.
   base::Lock clients_lock_;
 
   MidiPortInfoList input_ports_;
diff --git a/media/midi/midi_manager_alsa.cc b/media/midi/midi_manager_alsa.cc
index dd12fc0..c4be32f 100644
--- a/media/midi/midi_manager_alsa.cc
+++ b/media/midi/midi_manager_alsa.cc
@@ -10,7 +10,6 @@
 #include <string>
 
 #include "base/bind.h"
-#include "base/debug/trace_event.h"
 #include "base/logging.h"
 #include "base/memory/ref_counted.h"
 #include "base/message_loop/message_loop.h"
@@ -129,11 +128,7 @@ MidiManagerAlsa::MidiManagerAlsa()
     pipe_fd_[i] = -1;
 }
 
-MidiResult MidiManagerAlsa::Initialize() {
-  // TODO(toyoshim): Make Initialize() asynchronous.
-  // See http://crbug.com/339746.
-  TRACE_EVENT0("midi", "MidiManagerAlsa::Initialize");
-
+void MidiManagerAlsa::StartInitialization() {
   // Enumerate only hardware MIDI devices because software MIDIs running in
   // the browser process is not secure.
   snd_ctl_card_info_t* card;
@@ -190,14 +185,14 @@ MidiResult MidiManagerAlsa::Initialize() {
 
   if (pipe(pipe_fd_) < 0) {
     VPLOG(1) << "pipe() failed";
-    return MIDI_INITIALIZATION_ERROR;
+    CompleteInitialization(MIDI_INITIALIZATION_ERROR);
+  } else {
+    event_thread_.Start();
+    event_thread_.message_loop()->PostTask(
+        FROM_HERE,
+        base::Bind(&MidiManagerAlsa::EventReset, base::Unretained(this)));
+    CompleteInitialization(MIDI_OK);
   }
-  event_thread_.Start();
-  event_thread_.message_loop()->PostTask(
-      FROM_HERE,
-      base::Bind(&MidiManagerAlsa::EventReset, base::Unretained(this)));
-
-  return MIDI_OK;
 }
 
 MidiManagerAlsa::~MidiManagerAlsa() {
diff --git a/media/midi/midi_manager_alsa.h b/media/midi/midi_manager_alsa.h
index 803496b..04e1d09 100644
--- a/media/midi/midi_manager_alsa.h
+++ b/media/midi/midi_manager_alsa.h
@@ -21,7 +21,7 @@ class MidiManagerAlsa : public MidiManager {
   virtual ~MidiManagerAlsa();
 
   // MidiManager implementation.
-  virtual MidiResult Initialize() OVERRIDE;
+  virtual void StartInitialization() OVERRIDE;
   virtual void DispatchSendMidiData(MidiManagerClient* client,
                                     uint32 port_index,
                                     const std::vector<uint8>& data,
diff --git a/media/midi/midi_manager_mac.cc b/media/midi/midi_manager_mac.cc
index 0c9c869..c1302e6 100644
--- a/media/midi/midi_manager_mac.cc
+++ b/media/midi/midi_manager_mac.cc
@@ -6,7 +6,7 @@
 
 #include <string>
 
-#include "base/debug/trace_event.h"
+#include "base/bind.h"
 #include "base/message_loop/message_loop.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/sys_string_conversions.h"
@@ -36,19 +36,14 @@ MidiManagerMac::MidiManagerMac()
       send_thread_("MidiSendThread") {
 }
 
-MidiResult MidiManagerMac::Initialize() {
-  TRACE_EVENT0("midi", "MidiManagerMac::Initialize");
-
+void MidiManagerMac::StartInitialization() {
   // CoreMIDI registration.
   midi_client_ = 0;
-  OSStatus result = MIDIClientCreate(
-      CFSTR("Google Chrome"),
-      NULL,
-      NULL,
-      &midi_client_);
+  OSStatus result =
+      MIDIClientCreate(CFSTR("Chrome"), NULL, NULL, &midi_client_);
 
   if (result != noErr)
-    return MIDI_INITIALIZATION_ERROR;
+    return CompleteInitialization(MIDI_INITIALIZATION_ERROR);
 
   coremidi_input_ = 0;
 
@@ -60,14 +55,14 @@ MidiResult MidiManagerMac::Initialize() {
       this,
       &coremidi_input_);
   if (result != noErr)
-    return MIDI_INITIALIZATION_ERROR;
+    return CompleteInitialization(MIDI_INITIALIZATION_ERROR);
 
   result = MIDIOutputPortCreate(
       midi_client_,
       CFSTR("MIDI Output"),
       &coremidi_output_);
   if (result != noErr)
-    return MIDI_INITIALIZATION_ERROR;
+    return CompleteInitialization(MIDI_INITIALIZATION_ERROR);
 
   uint32 destination_count = MIDIGetNumberOfDestinations();
   destinations_.resize(destination_count);
@@ -98,11 +93,10 @@ MidiResult MidiManagerMac::Initialize() {
     AddInputPort(info);
   }
 
-  // TODO(toyoshim): Fix the memory management here!
   packet_list_ = reinterpret_cast<MIDIPacketList*>(midi_buffer_);
   midi_packet_ = MIDIPacketListInit(packet_list_);
 
-  return MIDI_OK;
+  CompleteInitialization(MIDI_OK);
 }
 
 void MidiManagerMac::DispatchSendMidiData(MidiManagerClient* client,
diff --git a/media/midi/midi_manager_mac.h b/media/midi/midi_manager_mac.h
index 5bd072d..5c514ff 100644
--- a/media/midi/midi_manager_mac.h
+++ b/media/midi/midi_manager_mac.h
@@ -24,7 +24,7 @@ class MEDIA_EXPORT MidiManagerMac : public MidiManager {
   virtual ~MidiManagerMac();
 
   // MidiManager implementation.
-  virtual MidiResult Initialize() OVERRIDE;
+  virtual void StartInitialization() OVERRIDE;
   virtual void DispatchSendMidiData(MidiManagerClient* client,
                                     uint32 port_index,
                                     const std::vector<uint8>& data,
diff --git a/media/midi/midi_manager_unittest.cc b/media/midi/midi_manager_unittest.cc
new file mode 100644
index 0000000..178b0f6
--- /dev/null
+++ b/media/midi/midi_manager_unittest.cc
@@ -0,0 +1,187 @@
+// Copyright 2014 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 "media/midi/midi_manager.h"
+
+#include "base/logging.h"
+#include "base/memory/scoped_ptr.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace media {
+
+namespace {
+
+class FakeMidiManager : public MidiManager {
+ public:
+  FakeMidiManager()
+      : start_initialization_is_called_(false),
+        complete_initialization_synchronously_(false) {}
+  virtual ~FakeMidiManager() {}
+
+  // MidiManager implementation.
+  virtual void StartInitialization() OVERRIDE {
+    start_initialization_is_called_ = true;
+    if (complete_initialization_synchronously_)
+      CompleteInitialization(MIDI_OK);
+  }
+
+  virtual void DispatchSendMidiData(MidiManagerClient* client,
+                                    uint32 port_index,
+                                    const std::vector<uint8>& data,
+                                    double timestamp) OVERRIDE {}
+
+  // Utility functions for testing.
+  void CallCompleteInitialization(MidiResult result) {
+    CompleteInitialization(result);
+  }
+
+  size_t GetClientCount() {
+    return clients_.size();
+  }
+
+  size_t GetPendingClientCount() {
+    return pending_clients_.size();
+  }
+
+  bool start_initialization_is_called_;
+  bool complete_initialization_synchronously_;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(FakeMidiManager);
+};
+
+class FakeMidiManagerClient : public MidiManagerClient {
+ public:
+  FakeMidiManagerClient(int client_id) : client_id_(client_id) {}
+  virtual ~FakeMidiManagerClient() {}
+
+  // MidiManagerClient implementation.
+  virtual void CompleteStartSession(int client_id, MidiResult result) OVERRIDE {
+    DCHECK_EQ(client_id_, client_id);
+    result_ = result;
+  }
+
+  virtual void ReceiveMidiData(uint32 port_index, const uint8* data,
+                               size_t size, double timestamp) OVERRIDE {}
+  virtual void AccumulateMidiBytesSent(size_t size) OVERRIDE {}
+
+  int GetClientId() {
+    return client_id_;
+  }
+
+  MidiResult GetResult() {
+    return result_;
+  }
+
+ private:
+  int client_id_;
+  MidiResult result_;
+
+  DISALLOW_COPY_AND_ASSIGN(FakeMidiManagerClient);
+};
+
+class MidiManagerTest : public ::testing::Test {
+ public:
+  MidiManagerTest() : manager_(new FakeMidiManager) {}
+  virtual ~MidiManagerTest() {}
+
+ protected:
+  void StartTheFirstSession(FakeMidiManagerClient* client,
+                            bool complete_initialization_synchronously) {
+    manager_->complete_initialization_synchronously_ =
+        complete_initialization_synchronously;
+    EXPECT_FALSE(manager_->start_initialization_is_called_);
+    EXPECT_EQ(0U, manager_->GetClientCount());
+    EXPECT_EQ(0U, manager_->GetPendingClientCount());
+    manager_->StartSession(client, client->GetClientId());
+    if (complete_initialization_synchronously) {
+      EXPECT_EQ(1U, manager_->GetClientCount());
+      EXPECT_EQ(0U, manager_->GetPendingClientCount());
+      EXPECT_TRUE(manager_->start_initialization_is_called_);
+      EXPECT_EQ(MIDI_OK, client->GetResult());
+    } else {
+      EXPECT_EQ(0U, manager_->GetClientCount());
+      EXPECT_EQ(1U, manager_->GetPendingClientCount());
+      EXPECT_TRUE(manager_->start_initialization_is_called_);
+      EXPECT_EQ(0U, manager_->GetClientCount());
+      EXPECT_EQ(1U, manager_->GetPendingClientCount());
+      EXPECT_TRUE(manager_->start_initialization_is_called_);
+    }
+  }
+
+  void StartTheSecondSession(FakeMidiManagerClient* client) {
+    EXPECT_TRUE(manager_->start_initialization_is_called_);
+    EXPECT_EQ(0U, manager_->GetClientCount());
+    EXPECT_EQ(1U, manager_->GetPendingClientCount());
+
+    // StartInitialization() should not be called for the second session.
+    manager_->start_initialization_is_called_ = false;
+    manager_->StartSession(client, client->GetClientId());
+    EXPECT_FALSE(manager_->start_initialization_is_called_);
+  }
+
+  void EndSession(FakeMidiManagerClient* client, size_t before, size_t after) {
+    EXPECT_EQ(before, manager_->GetClientCount());
+    manager_->EndSession(client);
+    EXPECT_EQ(after, manager_->GetClientCount());
+  }
+
+  void CompleteInitialization(MidiResult result) {
+    manager_->CallCompleteInitialization(result);
+  }
+
+ private:
+  scoped_ptr<FakeMidiManager> manager_;
+
+  DISALLOW_COPY_AND_ASSIGN(MidiManagerTest);
+};
+
+// Check if calling CompleteInitialization() does not acquire the same lock
+// on the same thread.
+TEST_F(MidiManagerTest, StartAndEndSessionSynchronously) {
+  scoped_ptr<FakeMidiManagerClient> client;
+  client.reset(new FakeMidiManagerClient(0));
+
+  StartTheFirstSession(client.get(), true);
+  EndSession(client.get(), 1U, 0U);
+}
+
+TEST_F(MidiManagerTest, StartAndEndSession) {
+  scoped_ptr<FakeMidiManagerClient> client;
+  client.reset(new FakeMidiManagerClient(0));
+
+  StartTheFirstSession(client.get(), false);
+  CompleteInitialization(MIDI_OK);
+  EXPECT_EQ(MIDI_OK, client->GetResult());
+  EndSession(client.get(), 1U, 0U);
+}
+
+TEST_F(MidiManagerTest, StartAndEndSessionWithError) {
+  scoped_ptr<FakeMidiManagerClient> client;
+  client.reset(new FakeMidiManagerClient(1));
+
+  StartTheFirstSession(client.get(), false);
+  CompleteInitialization(MIDI_INITIALIZATION_ERROR);
+  EXPECT_EQ(MIDI_INITIALIZATION_ERROR, client->GetResult());
+  EndSession(client.get(), 0U, 0U);
+}
+
+TEST_F(MidiManagerTest, StartMultipleSessions) {
+  scoped_ptr<FakeMidiManagerClient> client1;
+  scoped_ptr<FakeMidiManagerClient> client2;
+  client1.reset(new FakeMidiManagerClient(0));
+  client2.reset(new FakeMidiManagerClient(1));
+
+  StartTheFirstSession(client1.get(), false);
+  StartTheSecondSession(client2.get());
+  CompleteInitialization(MIDI_OK);
+  EXPECT_EQ(MIDI_OK, client1->GetResult());
+  EXPECT_EQ(MIDI_OK, client2->GetResult());
+  EndSession(client1.get(), 2U, 1U);
+  EndSession(client2.get(), 1U, 0U);
+}
+
+}  // namespace
+
+}  // namespace media
diff --git a/media/midi/midi_manager_usb.cc b/media/midi/midi_manager_usb.cc
index 3ac1dda..f2cf866 100644
--- a/media/midi/midi_manager_usb.cc
+++ b/media/midi/midi_manager_usb.cc
@@ -5,7 +5,6 @@
 #include "media/midi/midi_manager_usb.h"
 
 #include "base/callback.h"
-#include "base/debug/trace_event.h"
 #include "base/logging.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/message_loop/message_loop.h"
@@ -17,16 +16,6 @@
 
 namespace media {
 
-namespace {
-
-// Noop callback for (sync) Initialize.
-// TODO(yhirano): This function should go away when
-// MidiManager::Initialize() becomes asynchronous. See http://crbug.com/339746.
-void Noop(bool result) {
-}
-
-}  // namespace
-
 MidiManagerUsb::MidiManagerUsb(scoped_ptr<UsbMidiDevice::Factory> factory)
     : device_factory_(factory.Pass()) {
 }
@@ -34,13 +23,13 @@ MidiManagerUsb::MidiManagerUsb(scoped_ptr<UsbMidiDevice::Factory> factory)
 MidiManagerUsb::~MidiManagerUsb() {
 }
 
-MidiResult MidiManagerUsb::Initialize() {
-  TRACE_EVENT0("midi", "MidiManagerUsb::Initialize");
-  Initialize(base::Bind(Noop));
-  return MIDI_OK;
+void MidiManagerUsb::StartInitialization() {
+  Initialize(
+      base::Bind(&MidiManager::CompleteInitialization, base::Unretained(this)));
 }
 
-void MidiManagerUsb::Initialize(base::Callback<void(bool result)> callback) {
+void MidiManagerUsb::Initialize(
+    base::Callback<void(MidiResult result)> callback) {
   initialize_callback_ = callback;
   // This is safe because EnumerateDevices cancels the operation on destruction.
   device_factory_->EnumerateDevices(
@@ -83,7 +72,7 @@ void MidiManagerUsb::OnReceivedData(size_t jack_index,
 void MidiManagerUsb::OnEnumerateDevicesDone(bool result,
                                             UsbMidiDevice::Devices* devices) {
   if (!result) {
-    initialize_callback_.Run(false);
+    initialize_callback_.Run(MIDI_INITIALIZATION_ERROR);
     return;
   }
   devices->swap(devices_);
@@ -97,7 +86,7 @@ void MidiManagerUsb::OnEnumerateDevicesDone(bool result,
                                      descriptor.size(),
                                      &jacks);
     if (!parse_result) {
-      initialize_callback_.Run(false);
+      initialize_callback_.Run(MIDI_INITIALIZATION_ERROR);
       return;
     }
     std::vector<UsbMidiJack> input_jacks;
@@ -115,7 +104,7 @@ void MidiManagerUsb::OnEnumerateDevicesDone(bool result,
     }
     input_stream_.reset(new UsbMidiInputStream(input_jacks, this));
   }
-  initialize_callback_.Run(true);
+  initialize_callback_.Run(MIDI_OK);
 }
 
 }  // namespace media
diff --git a/media/midi/midi_manager_usb.h b/media/midi/midi_manager_usb.h
index 59548dd..694a051 100644
--- a/media/midi/midi_manager_usb.h
+++ b/media/midi/midi_manager_usb.h
@@ -32,7 +32,7 @@ class MEDIA_EXPORT MidiManagerUsb : public MidiManager,
   virtual ~MidiManagerUsb();
 
   // MidiManager implementation.
-  virtual MidiResult Initialize() OVERRIDE;
+  virtual void StartInitialization() OVERRIDE;
   virtual void DispatchSendMidiData(MidiManagerClient* client,
                                     uint32 port_index,
                                     const std::vector<uint8>& data,
@@ -61,7 +61,9 @@ class MEDIA_EXPORT MidiManagerUsb : public MidiManager,
   // result.
   // When this factory is destroyed during the operation, the operation
   // will be canceled silently (i.e. |callback| will not be called).
-  void Initialize(base::Callback<void(bool result)> callback);
+  // The function is public just for unit tests. Do not call this function
+  // outside code for testing.
+  void Initialize(base::Callback<void(MidiResult result)> callback);
 
  private:
   void OnEnumerateDevicesDone(bool result, UsbMidiDevice::Devices* devices);
@@ -71,7 +73,7 @@ class MEDIA_EXPORT MidiManagerUsb : public MidiManager,
   ScopedVector<UsbMidiOutputStream> output_streams_;
   scoped_ptr<UsbMidiInputStream> input_stream_;
 
-  base::Callback<void(bool result)> initialize_callback_;
+  base::Callback<void(MidiResult result)> initialize_callback_;
 
   // A map from <endpoint_number, cable_number> to the index of input jacks.
   base::hash_map<std::pair<int, int>, size_t> input_jack_dictionary_;
diff --git a/media/midi/midi_manager_usb_unittest.cc b/media/midi/midi_manager_usb_unittest.cc
index 4acc4c9..b9a2732 100644
--- a/media/midi/midi_manager_usb_unittest.cc
+++ b/media/midi/midi_manager_usb_unittest.cc
@@ -71,10 +71,15 @@ class FakeUsbMidiDevice : public UsbMidiDevice {
 
 class FakeMidiManagerClient : public MidiManagerClient {
  public:
-  explicit FakeMidiManagerClient(Logger* logger) : logger_(logger) {}
+  explicit FakeMidiManagerClient(Logger* logger)
+      : complete_start_session_(false),
+        result_(MIDI_NOT_SUPPORTED),
+        logger_(logger) {}
   virtual ~FakeMidiManagerClient() {}
 
   virtual void CompleteStartSession(int client_id, MidiResult result) OVERRIDE {
+    complete_start_session_ = true;
+    result_ = result;
   }
 
   virtual void ReceiveMidiData(uint32 port_index,
@@ -95,6 +100,9 @@ class FakeMidiManagerClient : public MidiManagerClient {
                                        static_cast<unsigned>(size)));
   }
 
+  bool complete_start_session_;
+  MidiResult result_;
+
  private:
   Logger* logger_;
 
@@ -116,14 +124,28 @@ class TestUsbMidiDeviceFactory : public UsbMidiDevice::Factory {
   DISALLOW_COPY_AND_ASSIGN(TestUsbMidiDeviceFactory);
 };
 
+class MidiManagerUsbForTesting : public MidiManagerUsb {
+ public:
+  explicit MidiManagerUsbForTesting(
+      scoped_ptr<UsbMidiDevice::Factory> device_factory)
+      : MidiManagerUsb(device_factory.PassAs<UsbMidiDevice::Factory>()) {}
+  virtual ~MidiManagerUsbForTesting() {}
+
+  void CallCompleteInitialization(MidiResult result) {
+    CompleteInitialization(result);
+  }
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(MidiManagerUsbForTesting);
+};
+
 class MidiManagerUsbTest : public ::testing::Test {
  public:
-  MidiManagerUsbTest()
-      : initialize_callback_run_(false), initialize_result_(false) {
+  MidiManagerUsbTest() {
     scoped_ptr<TestUsbMidiDeviceFactory> factory(new TestUsbMidiDeviceFactory);
     factory_ = factory.get();
     manager_.reset(
-        new MidiManagerUsb(factory.PassAs<UsbMidiDevice::Factory>()));
+        new MidiManagerUsbForTesting(factory.PassAs<UsbMidiDevice::Factory>()));
   }
   virtual ~MidiManagerUsbTest() {
     std::string leftover_logs = logger_.TakeLog();
@@ -134,19 +156,24 @@ class MidiManagerUsbTest : public ::testing::Test {
 
  protected:
   void Initialize() {
-    manager_->Initialize(base::Bind(&MidiManagerUsbTest::OnInitializeDone,
-                                    base::Unretained(this)));
+    client_.reset(new FakeMidiManagerClient(&logger_));
+    manager_->StartSession(client_.get(), 0);
+  }
+
+  void Finalize() {
+    manager_->EndSession(client_.get());
   }
 
-  void OnInitializeDone(bool result) {
-    initialize_callback_run_ = true;
-    initialize_result_ = result;
+  bool IsInitializationCallbackInvoked() {
+    return client_->complete_start_session_;
   }
 
-  bool initialize_callback_run_;
-  bool initialize_result_;
+  MidiResult GetInitializationResult() {
+    return client_->result_;
+  }
 
-  scoped_ptr<MidiManagerUsb> manager_;
+  scoped_ptr<MidiManagerUsbForTesting> manager_;
+  scoped_ptr<FakeMidiManagerClient> client_;
   // Owned by manager_.
   TestUsbMidiDeviceFactory* factory_;
   Logger logger_;
@@ -179,10 +206,10 @@ TEST_F(MidiManagerUsbTest, Initialize) {
   Initialize();
   ScopedVector<UsbMidiDevice> devices;
   devices.push_back(device.release());
-  EXPECT_FALSE(initialize_callback_run_);
+  EXPECT_FALSE(IsInitializationCallbackInvoked());
   factory_->callback_.Run(true, &devices);
-  EXPECT_TRUE(initialize_callback_run_);
-  EXPECT_TRUE(initialize_result_);
+  EXPECT_TRUE(IsInitializationCallbackInvoked());
+  EXPECT_EQ(MIDI_OK, GetInitializationResult());
 
   ASSERT_EQ(1u, manager_->input_ports().size());
   ASSERT_EQ(2u, manager_->output_ports().size());
@@ -201,10 +228,10 @@ TEST_F(MidiManagerUsbTest, Initialize) {
 TEST_F(MidiManagerUsbTest, InitializeFail) {
   Initialize();
 
-  EXPECT_FALSE(initialize_callback_run_);
+  EXPECT_FALSE(IsInitializationCallbackInvoked());
   factory_->callback_.Run(false, NULL);
-  EXPECT_TRUE(initialize_callback_run_);
-  EXPECT_FALSE(initialize_result_);
+  EXPECT_TRUE(IsInitializationCallbackInvoked());
+  EXPECT_EQ(MIDI_INITIALIZATION_ERROR, GetInitializationResult());
 }
 
 TEST_F(MidiManagerUsbTest, InitializeFailBecauseOfInvalidDescriptor) {
@@ -215,10 +242,10 @@ TEST_F(MidiManagerUsbTest, InitializeFailBecauseOfInvalidDescriptor) {
   Initialize();
   ScopedVector<UsbMidiDevice> devices;
   devices.push_back(device.release());
-  EXPECT_FALSE(initialize_callback_run_);
+  EXPECT_FALSE(IsInitializationCallbackInvoked());
   factory_->callback_.Run(true, &devices);
-  EXPECT_TRUE(initialize_callback_run_);
-  EXPECT_FALSE(initialize_result_);
+  EXPECT_TRUE(IsInitializationCallbackInvoked());
+  EXPECT_EQ(MIDI_INITIALIZATION_ERROR, GetInitializationResult());
   EXPECT_EQ("UsbMidiDevice::GetDescriptor\n", logger_.TakeLog());
 }
 
@@ -251,10 +278,10 @@ TEST_F(MidiManagerUsbTest, Send) {
   Initialize();
   ScopedVector<UsbMidiDevice> devices;
   devices.push_back(device.release());
-  EXPECT_FALSE(initialize_callback_run_);
+  EXPECT_FALSE(IsInitializationCallbackInvoked());
   factory_->callback_.Run(true, &devices);
-  ASSERT_TRUE(initialize_callback_run_);
-  ASSERT_TRUE(initialize_result_);
+  EXPECT_TRUE(IsInitializationCallbackInvoked());
+  EXPECT_EQ(MIDI_OK, GetInitializationResult());
   ASSERT_EQ(2u, manager_->output_streams().size());
 
   manager_->DispatchSendMidiData(&client, 1, ToVector(data), 0);
@@ -269,7 +296,6 @@ TEST_F(MidiManagerUsbTest, Send) {
 
 TEST_F(MidiManagerUsbTest, Receive) {
   scoped_ptr<FakeUsbMidiDevice> device(new FakeUsbMidiDevice(&logger_));
-  FakeMidiManagerClient client(&logger_);
   uint8 descriptor[] = {
     0x12, 0x01, 0x10, 0x01, 0x00, 0x00, 0x00, 0x08, 0x86, 0x1a,
     0x2d, 0x75, 0x54, 0x02, 0x00, 0x02, 0x00, 0x01, 0x09, 0x02,
@@ -299,15 +325,14 @@ TEST_F(MidiManagerUsbTest, Receive) {
   ScopedVector<UsbMidiDevice> devices;
   UsbMidiDevice* device_raw = device.get();
   devices.push_back(device.release());
-  EXPECT_FALSE(initialize_callback_run_);
+  EXPECT_FALSE(IsInitializationCallbackInvoked());
   factory_->callback_.Run(true, &devices);
-  ASSERT_TRUE(initialize_callback_run_);
-  ASSERT_TRUE(initialize_result_);
+  EXPECT_TRUE(IsInitializationCallbackInvoked());
+  EXPECT_EQ(MIDI_OK, GetInitializationResult());
 
-  manager_->StartSession(&client, 0);
   manager_->ReceiveUsbMidiData(device_raw, 2, data, arraysize(data),
                                base::TimeTicks());
-  manager_->EndSession(&client);
+  Finalize();
 
   EXPECT_EQ("UsbMidiDevice::GetDescriptor\n"
             "MidiManagerClient::ReceiveMidiData port_index = 0 "
diff --git a/media/midi/midi_manager_win.cc b/media/midi/midi_manager_win.cc
index d556e3a..a422299 100644
--- a/media/midi/midi_manager_win.cc
+++ b/media/midi/midi_manager_win.cc
@@ -21,7 +21,6 @@
 #include <algorithm>
 #include <string>
 #include "base/bind.h"
-#include "base/debug/trace_event.h"
 #include "base/message_loop/message_loop.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/utf_string_conversions.h"
@@ -497,8 +496,7 @@ MidiManagerWin::MidiManagerWin()
     : send_thread_("MidiSendThread") {
 }
 
-MidiResult MidiManagerWin::Initialize() {
-  TRACE_EVENT0("midi", "MidiManagerWin::Initialize");
+void MidiManagerWin::StartInitialization() {
   const UINT num_in_devices = midiInGetNumDevs();
   in_devices_.reserve(num_in_devices);
   for (UINT device_id = 0; device_id < num_in_devices; ++device_id) {
@@ -544,7 +542,7 @@ MidiResult MidiManagerWin::Initialize() {
     out_devices_.push_back(out_port.Pass());
   }
 
-  return MIDI_OK;
+  CompleteInitialization(MIDI_OK);
 }
 
 MidiManagerWin::~MidiManagerWin() {
diff --git a/media/midi/midi_manager_win.h b/media/midi/midi_manager_win.h
index 7b38ab4b..8a951f8 100644
--- a/media/midi/midi_manager_win.h
+++ b/media/midi/midi_manager_win.h
@@ -20,7 +20,7 @@ class MidiManagerWin : public MidiManager {
   virtual ~MidiManagerWin();
 
   // MidiManager implementation.
-  virtual MidiResult Initialize() OVERRIDE;
+  virtual void StartInitialization() OVERRIDE;
   virtual void DispatchSendMidiData(MidiManagerClient* client,
                                     uint32 port_index,
                                     const std::vector<uint8>& data,