Reland of "Decoupling rtc_base from Obj-C code"

webrtc/rtc_base/BUILD.gn

Index: webrtc/rtc_base/BUILD.gn
diff --git a/webrtc/rtc_base/BUILD.gn b/webrtc/rtc_base/BUILD.gn
index 6676fdf2eaf81043016c105a9cd83f150f701d4a..cc33b5155551bb33f67ef4376d164c3b3a8e8c6f 100644
--- a/webrtc/rtc_base/BUILD.gn
+++ b/webrtc/rtc_base/BUILD.gn
@@ -428,6 +428,27 @@ rtc_source_set("rtc_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 = []
@@ -537,6 +558,11 @@ rtc_static_library("rtc_base") {
     "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" ]
@@ -596,10 +622,7 @@ rtc_static_library("rtc_base") {
   }
 
   if (is_ios || is_mac) {
-    sources += [
-      "macifaddrs_converter.cc",
-      "thread_darwin.mm",
-    ]
+    sources += [ "macifaddrs_converter.cc" ]
   }
 
   if (use_x11) {