[tint] Move 'using namespace' into anonymous namespace

This avoids ambiguous overloads when system headers define something
with the same name as the imported namespace.

Change-Id: Icb32783ab89e7aa1076a4e292c6a6ef74b5529e9
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/137062
Reviewed-by: Dan Sinclair <dsinclair@chromium.org>
Commit-Queue: Ben Clayton <bclayton@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>
diff --git a/src/tint/resolver/variable_validation_test.cc b/src/tint/resolver/variable_validation_test.cc
index d29f8b0..44cc973 100644
--- a/src/tint/resolver/variable_validation_test.cc
+++ b/src/tint/resolver/variable_validation_test.cc
@@ -17,12 +17,12 @@
 #include "src/tint/resolver/resolver_test_helper.h"
 #include "src/tint/type/texture_dimension.h"
 
-using namespace tint::builtin::fluent_types;  // NOLINT
-using namespace tint::number_suffixes;        // NOLINT
-
 namespace tint::resolver {
 namespace {
 
+using namespace tint::builtin::fluent_types;  // NOLINT
+using namespace tint::number_suffixes;        // NOLINT
+
 struct ResolverVariableValidationTest : public resolver::TestHelper, public testing::Test {};
 
 TEST_F(ResolverVariableValidationTest, VarNoInitializerNoType) {