Make rtc_include_tests true by default in gn.

See bug for discussion.

BUG=webrtc:6119
TBR=kjellander@webrtc.org

Review-Url: https://codereview.webrtc.org/2156203002
Cr-Commit-Position: refs/heads/master@{#13500}

build_overrides/webrtc.gni

@@ -23,5 +23,7 @@ rtc_include_pulse_audio = true
 # standalone WebRTC.
 rtc_include_internal_audio_device = true
 
-# There's no point processing WebRTC standalone tests in a Chromium build.
-rtc_include_tests = true
+declare_args() {
+  # Include tests in standalone checkout.
+  rtc_include_tests = true
+}

webrtc/build/webrtc.gni

@@ -62,7 +62,6 @@ declare_args() {
   # https://gcc.gnu.org/wiki/LinkTimeOptimization
   rtc_use_lto = false
 
-  rtc_include_tests = false
   rtc_restrict_logging = true
 
   # Enable libevent task queues on platforms that support it.