Create a Promise class to simplify dealing with async results.

base/BUILD.gn

 # 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.
 
 # HOW TO WRITE CONDITIONALS IN THIS FILE
 # ======================================
 #
 # In many other places, one would write a conditional that expresses all the
 # cases when a source file is used or unused, and then either add or subtract
 # it from the sources list in that case
@@ skipping 2234 matching lines @@
       "android/java/src/org/chromium/base/LocaleUtils.java",
       "android/java/src/org/chromium/base/Log.java",
       "android/java/src/org/chromium/base/MemoryPressureListener.java",
       "android/java/src/org/chromium/base/ObserverList.java",
       "android/java/src/org/chromium/base/PackageUtils.java",
       "android/java/src/org/chromium/base/PathService.java",
       "android/java/src/org/chromium/base/PathUtils.java",
       "android/java/src/org/chromium/base/PerfTraceEvent.java",
       "android/java/src/org/chromium/base/PowerMonitor.java",
       "android/java/src/org/chromium/base/PowerStatusReceiver.java",
+      "android/java/src/org/chromium/base/Promise.java",
       "android/java/src/org/chromium/base/ResourceExtractor.java",
       "android/java/src/org/chromium/base/SecureRandomInitializer.java",
       "android/java/src/org/chromium/base/StreamUtil.java",
       "android/java/src/org/chromium/base/SysUtils.java",
       "android/java/src/org/chromium/base/SystemMessageHandler.java",
       "android/java/src/org/chromium/base/ThreadUtils.java",
       "android/java/src/org/chromium/base/TraceEvent.java",
       "android/java/src/org/chromium/base/VisibleForTesting.java",
       "android/java/src/org/chromium/base/annotations/AccessedByNative.java",
       "android/java/src/org/chromium/base/annotations/CalledByNative.java",
@@ skipping 98 matching lines @@
       "//third_party/robolectric:robolectric_java",
     ]
     srcjar_deps = [ ":base_build_config_gen" ]
   }
 
   # GYP: //base.gyp:base_junit_tests
   junit_binary("base_junit_tests") {
     java_files = [
       "android/junit/src/org/chromium/base/BaseChromiumApplicationTest.java",
       "android/junit/src/org/chromium/base/LogTest.java",
+      "android/junit/src/org/chromium/base/PromiseTest.java",
       "test/android/junit/src/org/chromium/base/test/util/DisableIfTest.java",
       "test/android/junit/src/org/chromium/base/test/util/MinAndroidSdkLevelSkipCheckTest.java",
       "test/android/junit/src/org/chromium/base/test/util/RestrictionSkipCheckTest.java",
       "test/android/junit/src/org/chromium/base/test/util/SkipCheckTest.java",
     ]
     deps = [
       ":base_java",
       ":base_java_test_support",
       ":base_junit_test_support",
     ]
@@ skipping 35 matching lines @@
 
   # GYP: //base.gyp:base_java_unittest_support
   android_library("base_java_unittest_support") {
     deps = [
       ":base_java",
     ]
     java_files =
         [ "test/android/java/src/org/chromium/base/ContentUriTestUtils.java" ]
   }
 }