Revert "Delete reference to webrtc_overides/rtc_base/task_queue.cc."

This reverts commit 17a0474379ebba7f48a59f2952b0a184071c47d8.

Reason for revert: Blocks roll into chromium. The Chromium CL this depends on was reverted.

Original change's description:
> Delete reference to webrtc_overides/rtc_base/task_queue.cc.
> 
> This change depends on Chromium cl
> https://chromium-review.googlesource.com/c/chromium/src/+/681814,
> which must be landed first.
> 
> Bug: webrtc:8166
> Change-Id: I8e1c96ad5927e1d9d4e45e6f6c0b5f712d58cef7
> Reviewed-on: https://webrtc-review.googlesource.com/3940
> Reviewed-by: Henrik Kjellander <kjellander@webrtc.org>
> Reviewed-by: Per Kjellander <perkj@webrtc.org>
> Commit-Queue: Niels Moller <nisse@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#20071}

TBR=kjellander@webrtc.org,nisse@webrtc.org,perkj@webrtc.org

Change-Id: I8bf5a27adb6549c70d9e2b632dfeaf23fab3cdd2
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: webrtc:8166
Reviewed-on: https://webrtc-review.googlesource.com/5740
Reviewed-by: Henrik Boström <hbos@webrtc.org>
Commit-Queue: Henrik Boström <hbos@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20103}
diff --git a/rtc_base/BUILD.gn b/rtc_base/BUILD.gn
index cf6ff94..93f8990 100644
--- a/rtc_base/BUILD.gn
+++ b/rtc_base/BUILD.gn
@@ -345,26 +345,32 @@
     ":rtc_base_approved",
     ":rtc_task_queue_api",
   ]
-  if (rtc_build_libevent) {
-    deps += [ "//base/third_party/libevent" ]
-  }
-  if (rtc_enable_libevent) {
+  if (build_with_chromium) {
     sources = [
-      "task_queue_libevent.cc",
-      "task_queue_posix.cc",
-      "task_queue_posix.h",
+      "../../webrtc_overrides/rtc_base/task_queue.cc",
     ]
   } else {
-    if (is_mac || is_ios) {
-      sources = [
-        "task_queue_gcd.cc",
-        "task_queue_posix.cc",
-      ]
+    if (rtc_build_libevent) {
+      deps += [ "//base/third_party/libevent" ]
     }
-    if (is_win) {
+    if (rtc_enable_libevent) {
       sources = [
-        "task_queue_win.cc",
+        "task_queue_libevent.cc",
+        "task_queue_posix.cc",
+        "task_queue_posix.h",
       ]
+    } else {
+      if (is_mac || is_ios) {
+        sources = [
+          "task_queue_gcd.cc",
+          "task_queue_posix.cc",
+        ]
+      }
+      if (is_win) {
+        sources = [
+          "task_queue_win.cc",
+        ]
+      }
     }
   }
 }