[Bluetooth, Performance] Cache the Bluetooth adapter name on Mac.

device/bluetooth/bluetooth_adapter_mac.mm

 // 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 "device/bluetooth/bluetooth_adapter_mac.h"
 
 #import <IOBluetooth/objc/IOBluetoothDevice.h>
 #import <IOBluetooth/objc/IOBluetoothHostController.h>
 
 #include <string>
@@ skipping 234 matching lines @@
   PollAdapter();
 }
 
 void BluetoothAdapterMac::PollAdapter() {
   // TODO(erikchen): Remove ScopedTracker below once http://crbug.com/461181
   // is fixed.
   tracked_objects::ScopedTracker tracking_profile1(
       FROM_HERE_WITH_EXPLICIT_FUNCTION(
           "461181 BluetoothAdapterMac::PollAdapter::Start"));
   bool was_present = IsPresent();
-  std::string name;
   std::string address;
   bool powered = false;
   IOBluetoothHostController* controller =
       [IOBluetoothHostController defaultController];
 
   // TODO(erikchen): Remove ScopedTracker below once http://crbug.com/461181
   // is fixed.
   tracked_objects::ScopedTracker tracking_profile2(
       FROM_HERE_WITH_EXPLICIT_FUNCTION(
           "461181 BluetoothAdapterMac::PollAdapter::GetControllerStats"));
   if (controller != nil) {
-    name = base::SysNSStringToUTF8([controller nameAsString]);
     address = BluetoothDevice::CanonicalizeAddress(
         base::SysNSStringToUTF8([controller addressAsString]));
     powered = ([controller powerState] == kBluetoothHCIPowerStateON);
+
+    // For performance reasons, cache the adapter's name. It's not uncommon for
+    // a call to [controller nameAsString] to take tens of milliseconds. Note
+    // that this caching strategy might result in clients receiving a stale
+    // name. If this is a significant issue, then some more sophisticated
+    // workaround for the performance bottleneck will be needed. For additional
+    // context, see http://crbug.com/461181 and http://crbug.com/467316
+    if (address != address_ || (!address.empty() && name_.empty()))
+      name_ = base::SysNSStringToUTF8([controller nameAsString]);
   }
 
   bool is_present = !address.empty();
-  name_ = name;
   address_ = address;
 
   // TODO(erikchen): Remove ScopedTracker below once http://crbug.com/461181
   // is fixed.
   tracked_objects::ScopedTracker tracking_profile3(
       FROM_HERE_WITH_EXPLICIT_FUNCTION(
           "461181 BluetoothAdapterMac::PollAdapter::AdapterPresentChanged"));
   if (was_present != is_present) {
     FOR_EACH_OBSERVER(BluetoothAdapter::Observer, observers_,
                       AdapterPresentChanged(this, is_present));
@@ skipping 64 matching lines @@
     DCHECK_EQ(num_removed, 1U);
   }
 
   // Add any new paired devices.
   for (IOBluetoothDevice* device in [IOBluetoothDevice pairedDevices]) {
     DeviceAdded(device);
   }
 }
 
 }  // namespace device