gn: Do not include "webrtc" in Chromium/iOS builds.

It's not part of the gyp build either, and `ninja -C out/gnios webrtc`
causes several build errors, at least in Chromium builds (which means
gn/ios bots building 'all' are broken).

BUG=chromium:633316
R=kjellander@webrtc.org

Review URL: https://codereview.webrtc.org/2205533003 .

Cr-Commit-Position: refs/heads/master@{#13609}

webrtc/BUILD.gn

@@ -240,47 +240,49 @@ config("common_objc") {
   precompiled_source = "sdk/objc/WebRTC-Prefix.pch"
 }
 
-source_set("webrtc") {
-  sources = [
-    "call.h",
-    "config.h",
-    "transport.h",
-  ]
-
-  defines = []
-  configs += [ ":common_config" ]
-  public_configs = [ ":common_inherited_config" ]
-
-  deps = [
-    ":webrtc_common",
-    "audio",
-    "base:rtc_base",
-    "call",
-    "common_audio",
-    "common_video",
-    "modules",
-    "system_wrappers",
-    "tools",
-    "video",
-    "voice_engine",
-  ]
-
-  if (build_with_chromium) {
-    deps += [ "modules/video_capture" ]
-  } else {
-    # TODO(kjellander): Enable for Chromium as well when bugs.webrtc.org/4256 is
-    # fixed. Right now it's not possible due to circular dependencies.
-    deps += [
-      "api",
-      "media",
-      "p2p",
-      "pc",
+if (!is_ios || !build_with_chromium) {
+  source_set("webrtc") {
+    sources = [
+      "call.h",
+      "config.h",
+      "transport.h",
     ]
-  }
 
-  if (rtc_enable_protobuf) {
-    defines += [ "ENABLE_RTC_EVENT_LOG" ]
-    deps += [ ":rtc_event_log_proto" ]
+    defines = []
+    configs += [ ":common_config" ]
+    public_configs = [ ":common_inherited_config" ]
+
+    deps = [
+      ":webrtc_common",
+      "audio",
+      "base:rtc_base",
+      "call",
+      "common_audio",
+      "common_video",
+      "modules",
+      "system_wrappers",
+      "tools",
+      "video",
+      "voice_engine",
+    ]
+
+    if (build_with_chromium) {
+      deps += [ "modules/video_capture" ]
+    } else {
+      # TODO(kjellander): Enable for Chromium as well when bugs.webrtc.org/4256
+      # is fixed. Right now it's not possible due to circular dependencies.
+      deps += [
+        "api",
+        "media",
+        "p2p",
+        "pc",
+      ]
+    }
+
+    if (rtc_enable_protobuf) {
+      defines += [ "ENABLE_RTC_EVENT_LOG" ]
+      deps += [ ":rtc_event_log_proto" ]
+    }
   }
 }