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

webrtc/base/base.gyp

Index: webrtc/base/base.gyp
diff --git a/webrtc/base/base.gyp b/webrtc/base/base.gyp
index 74b029c1f7a7bb32a8267e5f4fbdaae68936a113..13234e3145092f30989b6440e79aa7d56d7f631b 100644
--- a/webrtc/base/base.gyp
+++ b/webrtc/base/base.gyp
@@ -84,6 +84,12 @@
         'swap_queue.h',
         'systeminfo.cc',
         'systeminfo.h',
+        'task_queue.h',
+        'task_queue_libevent.cc',
+        'task_queue_gcd.cc',
+        'task_queue_posix.cc',
+        'task_queue_posix.h',
+        'task_queue_win.cc',
         'template_util.h',
         'thread_annotations.h',
         'thread_checker.h',
@@ -111,6 +117,19 @@
             'logging.h',
             'logging_mac.mm',
           ],
+          'conditions': [
+            ['build_libevent==1', {
+              'dependencies': [
+                '<(DEPTH)/base/third_party/libevent/libevent.gyp:libevent',
+              ],
+            }],
+          ],
+        }],
+        ['build_libevent!=1', {
+          'sources!': [ 'task_queue_libevent.cc' ],
+        }],
+        ['build_libevent==1 or OS=="linux" or OS=="android" or OS=="win"', {
+          'sources!': [ 'task_queue_gcd.cc' ],
         }],
         ['OS=="mac" and build_with_chromium==0', {
           'all_dependent_settings': {