Reland of New task queueing primitive for async tasks: TaskQueue.

webrtc/base/BUILD.gn

 # Copyright (c) 2014 The WebRTC project authors. All Rights Reserved.
 #
 # Use of this source code is governed by a BSD-style license
 # that can be found in the LICENSE file in the root of the source
 # tree. An additional intellectual property rights grant can be found
 # in the file PATENTS.  All contributing project authors may
 # be found in the AUTHORS file in the root of the source tree.
 
 import("//build/config/crypto.gni")
 import("//build/config/ui.gni")
@@ skipping 68 matching lines @@
 if (rtc_build_ssl == 0) {
   config("external_ssl_library") {
     assert(rtc_ssl_root != "",
            "You must specify rtc_ssl_root when rtc_build_ssl==0.")
     include_dirs = [ rtc_ssl_root ]
   }
 }
 
 # The subset of rtc_base approved for use outside of libjingle.
 static_library("rtc_base_approved") {
+  defines = []
   deps = []
   configs += [ "..:common_config" ]
   public_configs = [ "..:common_inherited_config" ]
   all_dependent_configs = [ ":rtc_base_approved_all_dependent_config" ]
 
   sources = [
     "array_view.h",
     "atomicops.h",
     "bind.h",
     "bitbuffer.cc",
@@ skipping 41 matching lines @@
     "safe_conversions_impl.h",
     "scoped_ptr.h",
     "scoped_ref_ptr.h",
     "stringencode.cc",
     "stringencode.h",
     "stringutils.cc",
     "stringutils.h",
     "swap_queue.h",
     "systeminfo.cc",
     "systeminfo.h",
+    "task_queue.h",
+    "task_queue_gcd.cc",
+    "task_queue_libevent.cc",
+    "task_queue_posix.cc",
+    "task_queue_posix.h",
+    "task_queue_win.cc",
     "template_util.h",
     "thread_annotations.h",
     "thread_checker.h",
     "thread_checker_impl.cc",
     "thread_checker_impl.h",
     "timeutils.cc",
     "timeutils.h",
     "trace_event.h",
   ]
 
   if (build_with_chromium) {
     # Dependency on chromium's logging (in //base).
     deps += [ "//base:base" ]
     sources += [
       "../../webrtc_overrides/webrtc/base/logging.cc",
       "../../webrtc_overrides/webrtc/base/logging.h",
     ]
     include_dirs = [ "../../webrtc_overrides" ]
   } else {
     sources += [
       "logging.cc",
       "logging.h",
       "logging_mac.mm",
     ]
   }
+
+  if (!is_win && !is_mac && !is_ios && !is_nacl) {

[kjellander_webrtc, 2016/05/16 12:25:50]

For GN, please introduce the same variables as for the GYP build, in
webrtc/build/webrtc.gni.

+    deps += [ "//base/third_party/libevent" ]
+    defines += [ "WEBRTC_BUILD_LIBEVENT" ]
+  }
+
+  if (is_mac || is_ios || is_win || is_nacl) {
+    sources -= [ "task_queue_libevent.cc" ]

[kjellander_webrtc, 2016/05/16 12:25:50]

Please only add to sources, i.e. avoid using subtraction from sources listings
(applies to GYP as well).
I've spend a fair amount of time cleaning up webrtc/base from this (see  
https://codereview.webrtc.org/1857163003 for a painful CL) and I don't want to
see it regress again. Maintenance become very cumbersome and error prone.

+  }
+
+  if (is_linux || is_android || is_win || is_nacl) {
+    sources -= [ "task_queue_gcd.cc" ]
+  }
+
+  if (is_nacl) {
+    sources -= [ "task_queue_posix.cc" ]
+  }
 }
 
 static_library("rtc_base") {
   cflags = []
   cflags_cc = []
   libs = []
   deps = [
     "..:webrtc_common",
   ]
   public_deps = [
@@ skipping 403 matching lines @@
     defines += [ "timezone=_timezone" ]
     sources -= [ "ifaddrs_converter.cc" ]
   }
 }
 
 source_set("gtest_prod") {
   sources = [
     "gtest_prod_util.h",
   ]
 }