Reland of "Decoupling rtc_base from Obj-C code"

webrtc/rtc_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 410 matching lines @@
   } else {
     include_dirs = [ "$rtc_jsoncpp_root" ]
 
     # When defined changes the include path for json.h to where it is
     # expected to be when building json outside of the standalone build.
     defines += [ "WEBRTC_EXTERNAL_JSON" ]
   }
 }
 
 rtc_static_library("rtc_base") {
+  public_deps = [

[kjellander_webrtc, 2017/09/06 17:59:36]

So the generic target is made to avoid the cyclic dependency error, right?

I think you have three options here if we want this to work then:
1) add a noop.cc file to satisfy linking for static library, it fails if there
isn't any source.
2) move only the parts that are involved in the cycle to generic and keep other
source in rtc_base, but that's quite confusing.
3) just disable gn check for the rtc_base_objc target.

+    ":rtc_base_generic",
+  ]
+  if (is_ios || is_mac) {
+    public_deps += [ ":rtc_base_objc" ]
+  }
+}
+
+if (is_ios || is_mac) {
+  rtc_source_set("rtc_base_objc") {
+    sources = [
+      "thread_darwin.mm",
+    ]
+    deps = [
+      ":rtc_base_generic",
+    ]
+    visibility = [ ":rtc_base" ]
+  }
+}
+
+rtc_static_library("rtc_base_generic") {
   cflags = []
   cflags_cc = []
   libs = []
   defines = []
   deps = [
     "..:webrtc_common",
     "../api:optional",
   ]
   public_deps = [
     ":rtc_base_approved",
@@ skipping 89 matching lines @@
     "sslidentity.cc",
     "sslidentity.h",
     "sslstreamadapter.cc",
     "sslstreamadapter.h",
     "stream.cc",
     "stream.h",
     "thread.cc",
     "thread.h",
   ]
 
+  visibility = [
+    ":rtc_base",
+    ":rtc_base_objc",
+  ]
+
   # TODO(henrike): issue 3307, make rtc_base build with the Chromium default
   # compiler settings.
   suppressed_configs += [ "//build/config/compiler:chromium_code" ]
   configs += [ "//build/config/compiler:no_chromium_code" ]
   if (!is_win) {
     cflags += [ "-Wno-uninitialized" ]
   }
 
   if (build_with_chromium) {
     if (is_win) {
@@ skipping 39 matching lines @@
       "ifaddrs-android.h",
     ]
 
     libs += [
       "log",
       "GLESv2",
     ]
   }
 
   if (is_ios || is_mac) {
-    sources += [
-      "macifaddrs_converter.cc",
-      "thread_darwin.mm",
-    ]
+    sources += [ "macifaddrs_converter.cc" ]
   }
 
   if (use_x11) {
     libs += [
       "dl",
       "rt",
       "Xext",
       "X11",
       "Xcomposite",
       "Xrender",
@@ skipping 460 matching lines @@
       "java/src/org/webrtc/ContextUtils.java",
       "java/src/org/webrtc/Logging.java",
       "java/src/org/webrtc/Size.java",
       "java/src/org/webrtc/ThreadUtils.java",
     ]
 
     # TODO(sakal): Fix build hooks crbug.com/webrtc/8148
     no_build_hooks = true
   }
 }