Replace WTF::Optional the base::Optional implementation.

build/config/compiler/BUILD.gn

Index: build/config/compiler/BUILD.gn
diff --git a/build/config/compiler/BUILD.gn b/build/config/compiler/BUILD.gn
index 07408d69c64d67f4159ae5b371295b97150f43a4..cf6d8c72da5774522ad0ab713619c1df4453f5b2 100644
--- a/build/config/compiler/BUILD.gn
+++ b/build/config/compiler/BUILD.gn
@@ -914,6 +914,10 @@ config("default_warnings") {
       # for gcc 4.8.
       # TODO: remove this flag once all builds work. See crbug.com/227506
       cflags += [ "-Wno-unused-local-typedefs" ]
+
+      # Don't warn about "maybe" uninitialized. Clang doesn't include this
+      # in -Wall but gcc does, and it gives false positives.
+      cflags += [ "-Wno-maybe-uninitialized" ]
     }
   }