Add dvlog_always_on to enable DVLOG without DEBUG and DCHECK option

build/config/BUILD.gn

Index: build/config/BUILD.gn
diff --git a/build/config/BUILD.gn b/build/config/BUILD.gn
index a0b492740da8a6030e5291da234260d1cde4327f..9b2118b6d8778146dbc1f09b248d56d845c11a62 100644
--- a/build/config/BUILD.gn
+++ b/build/config/BUILD.gn
@@ -8,6 +8,7 @@ import("//build/config/chrome_build.gni")
 import("//build/config/chromecast_build.gni")
 import("//build/config/crypto.gni")
 import("//build/config/dcheck_always_on.gni")
+import("//build/config/dvlog_always_on.gni")
 import("//build/config/features.gni")
 import("//build/config/pch.gni")
 import("//build/config/sanitizers/sanitizers.gni")
@@ -54,6 +55,9 @@ config("feature_flags") {
   if (dcheck_always_on) {
     defines += [ "DCHECK_ALWAYS_ON=1" ]
   }
+  if (dvlog_always_on) {
+    defines += [ "DVLOG_ALWAYS_ON=1" ]
+  }
   if (use_udev) {
     # TODO(brettw) should probably be "=1".
     defines += [ "USE_UDEV" ]