Prevent GetDeviceId from invoking its callback multiple times in failure cases.

chrome/browser/extensions/api/music_manager_private/device_id.cc

 // 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/extensions/api/music_manager_private/device_id.h"
 
 #include "base/bind.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/string_util.h"
 #include "content/public/browser/browser_thread.h"
@@ skipping 17 matching lines @@
   return result;
 }
 
 void GetMachineIdCallback(const std::string& extension_id,
                           const extensions::api::DeviceId::IdCallback& callback,
                           const std::string& machine_id) {
   DCHECK(content::BrowserThread::CurrentlyOn(content::BrowserThread::UI));
 
   if (machine_id.empty()) {
     callback.Run("");
+    return;
   }
 
   std::string device_id;
   if (!ComputeHmacSha256(machine_id, extension_id, &device_id)) {
     DLOG(ERROR) << "Error while computing HMAC-SHA256 of device id.";
     callback.Run("");
+    return;
   }
   callback.Run(device_id);
 }
 
-}
+}  // namespace
 
 namespace extensions {
 namespace api {
 
 /* static */
 void DeviceId::GetDeviceId(const std::string& extension_id,
                            const IdCallback& callback) {
   DCHECK(content::BrowserThread::CurrentlyOn(content::BrowserThread::UI));
   CHECK(!extension_id.empty());
 
   // Forward call to platform specific implementation, then compute the HMAC
   // in the callback.
   GetMachineId(base::Bind(&GetMachineIdCallback, extension_id, callback));
 }
 
 }  // namespace api
 }  // namespace extensions