Remove non-monotonic clock support

webrtc/system_wrappers/BUILD.gn

Index: webrtc/system_wrappers/BUILD.gn
diff --git a/webrtc/system_wrappers/BUILD.gn b/webrtc/system_wrappers/BUILD.gn
index 004d9d2343c0bbdd35b836787c1f63839e311e47..9ed4dee0b613e1a88ab6b00fc2a2d4fba192fc6a 100644
--- a/webrtc/system_wrappers/BUILD.gn
+++ b/webrtc/system_wrappers/BUILD.gn
@@ -100,15 +100,7 @@ static_library("system_wrappers") {
       "source/logcat_trace_context.cc",
     ]
 
-    defines += [
-      "WEBRTC_THREAD_RR",
-
-      # TODO(leozwang): Investigate CLOCK_REALTIME and CLOCK_MONOTONIC
-      # support on Android. Keep WEBRTC_CLOCK_TYPE_REALTIME for now,
-      # remove it after I verify that CLOCK_MONOTONIC is fully functional
-      # with condition and event functions in system_wrappers.
-      "WEBRTC_CLOCK_TYPE_REALTIME",
-    ]
+    defines += [ "WEBRTC_THREAD_RR" ]
 
     deps += [ ":cpu_features_android" ]
 
@@ -116,12 +108,7 @@ static_library("system_wrappers") {
   }
 
   if (is_linux) {
-    defines += [
-      "WEBRTC_THREAD_RR",
-      # TODO(andrew): can we select this automatically?
-      # Define this if the Linux system does not support CLOCK_MONOTONIC.
-      #"WEBRTC_CLOCK_TYPE_REALTIME",
-    ]
+    defines += [ "WEBRTC_THREAD_RR" ]
 
     libs += [ "rt" ]
   }
@@ -131,10 +118,7 @@ static_library("system_wrappers") {
   }
 
   if (is_ios || is_mac) {
-    defines += [
-      "WEBRTC_THREAD_RR",
-      "WEBRTC_CLOCK_TYPE_REALTIME",
-    ]
+    defines += [ "WEBRTC_THREAD_RR" ]
   }
 
   if (is_ios) {