Audit GN cflags and defines to match GYP build.

build/config/BUILD.gn

Index: build/config/BUILD.gn
diff --git a/build/config/BUILD.gn b/build/config/BUILD.gn
index 49b5cfeb6a58ca05cd1c7395d1c67343888ba39a..7d7a56c10b9c04fa4447854739aace58ef37e250 100644
--- a/build/config/BUILD.gn
+++ b/build/config/BUILD.gn
@@ -14,11 +14,16 @@ declare_args() {
   # catching bugs but in some cases may cause conflicts or excessive slowness.
   disable_iterator_debugging = false
 
-  # Set to true to not store any build metadata (this isn't working yet but
-  # this flag will help us to get there). See http://crbug.com/314403.
-  # TODO(sebmarchand): Update this comment once this flag guarantee that
-  #     there's no build metadata in the build artifacts.
-  dont_embed_build_metadata = false
+  # Set to true to not store any build metadata, e.g. ifdef out all __DATE__
+  # and __TIME__. Set to 0 to reenable the use of these macros in the code
+  # base. See http://crbug.com/314403.
+  #
+  # Continue to embed build meta data in Official builds, basically the
+  # time it was built.
+  # TODO(maruel): This decision should be revisited because having an
+  # official deterministic build has high value too but MSVC toolset can't
+  # generate anything deterministic with WPO enabled AFAIK.
+  dont_embed_build_metadata = is_official_build
 
   # Set to true to enable dcheck in Release builds.
   dcheck_always_on = false
@@ -214,6 +219,12 @@ config("feature_flags") {
   if (v8_use_external_startup_data) {
     defines += [ "V8_USE_EXTERNAL_STARTUP_DATA" ]
   }
+  if (enable_background) {
+    defines += [ "ENABLE_BACKGROUND=1" ]
+  }
+  if (enable_pre_sync_backup) {
+    defines += [ "ENABLE_PRE_SYNC_BACKUP" ]
+  }
 }
 
 # Debug/release ----------------------------------------------------------------