Create a reader-writer lock implementaiton in base.

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 714 matching lines @@
     "synchronization/cancellation_flag.cc",
     "synchronization/cancellation_flag.h",
     "synchronization/condition_variable.h",
     "synchronization/condition_variable_posix.cc",
     "synchronization/condition_variable_win.cc",
     "synchronization/lock.cc",
     "synchronization/lock.h",
     "synchronization/lock_impl.h",
     "synchronization/lock_impl_posix.cc",
     "synchronization/lock_impl_win.cc",
+    "synchronization/read_write_lock.h",
+    "synchronization/read_write_lock_nacl.cc",
+    "synchronization/read_write_lock_posix.cc",
+    "synchronization/read_write_lock_win.cc",
     "synchronization/spin_wait.h",
     "synchronization/waitable_event.h",
     "synchronization/waitable_event_posix.cc",
     "synchronization/waitable_event_watcher.h",
     "synchronization/waitable_event_watcher_posix.cc",
     "synchronization/waitable_event_watcher_win.cc",
     "synchronization/waitable_event_win.cc",
     "sys_byteorder.h",
     "sys_info.cc",
     "sys_info.h",
@@ skipping 372 matching lines @@
       "process/kill.h",
       "process/memory.cc",
       "process/memory.h",
       "process/process_iterator.cc",
       "process/process_iterator.h",
       "process/process_metrics.cc",
       "process/process_metrics_posix.cc",
       "process/process_posix.cc",
       "scoped_native_library.cc",
       "sync_socket_posix.cc",
+      "synchronization/read_write_lock_posix.cc",
       "sys_info.cc",
       "sys_info_posix.cc",
       "trace_event/trace_event_system_stats_monitor.cc",
     ]
 
     if (is_nacl_nonsfi) {
       set_sources_assignment_filter([])
       sources += [ "posix/unix_domain_socket_linux.cc" ]
       set_sources_assignment_filter(sources_assignment_filter)
       sources -= [ "rand_util_nacl.cc" ]
@@ skipping 14 matching lines @@
         "rand_util_posix.cc",
       ]
     }
   } else {
     # Remove NaCl stuff.
     sources -= [
       "memory/shared_memory_nacl.cc",
       "os_compat_nacl.cc",
       "os_compat_nacl.h",
       "rand_util_nacl.cc",
+      "synchronization/read_write_lock_nacl.cc",
     ]
   }
 
   # Windows.
   if (is_win) {
     sources += [
       "profiler/win32_stack_frame_unwinder.cc",
       "profiler/win32_stack_frame_unwinder.h",
     ]
 
@@ skipping 676 matching lines @@
     "strings/stringprintf_unittest.cc",
     "strings/sys_string_conversions_mac_unittest.mm",
     "strings/sys_string_conversions_unittest.cc",
     "strings/utf_offset_string_conversions_unittest.cc",
     "strings/utf_string_conversions_unittest.cc",
     "supports_user_data_unittest.cc",
     "sync_socket_unittest.cc",
     "synchronization/cancellation_flag_unittest.cc",
     "synchronization/condition_variable_unittest.cc",
     "synchronization/lock_unittest.cc",
+    "synchronization/read_write_lock_unittest.cc",
     "synchronization/waitable_event_unittest.cc",
     "synchronization/waitable_event_watcher_unittest.cc",
     "sys_info_unittest.cc",
     "system_monitor/system_monitor_unittest.cc",
     "task/cancelable_task_tracker_unittest.cc",
     "task_runner_util_unittest.cc",
     "task_scheduler/delayed_task_manager_unittest.cc",
     "task_scheduler/priority_queue_unittest.cc",
     "task_scheduler/scheduler_lock_unittest.cc",
     "task_scheduler/scheduler_service_thread_unittest.cc",
@@ skipping 509 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" ]
   }
 }