Reland of move some warning suppressions from SocketRocket.

webrtc/examples/BUILD.gn

Index: webrtc/examples/BUILD.gn
diff --git a/webrtc/examples/BUILD.gn b/webrtc/examples/BUILD.gn
index 0098d69781b72a4ca416a826ed4cdf85142d9cea..d575c65b09fcec9793564c345d7e5864320c43b6 100644
--- a/webrtc/examples/BUILD.gn
+++ b/webrtc/examples/BUILD.gn
@@ -399,10 +399,6 @@ if (is_ios || (is_mac && target_cpu != "x86")) {
     cflags_objc = [
       # Enabled for cflags_objc in build/config/compiler/BUILD.gn.
       "-Wno-objc-missing-property-synthesis",
-
-      # Hide the warning for SecRandomCopyBytes(), until we update to upstream.
-      # https://bugs.chromium.org/p/webrtc/issues/detail?id=6396
-      "-Wno-unused-result",
     ]
   }