[presubmit] Enable readability/namespace linter checking.

src/x64/code-stubs-x64.h

Index: src/x64/code-stubs-x64.h
diff --git a/src/x64/code-stubs-x64.h b/src/x64/code-stubs-x64.h
index 1344400d48eff7f70642b8cb621d00dfa3f7cf75..4e3715b0e1282219542c96d8d9e9aad693ce37be 100644
--- a/src/x64/code-stubs-x64.h
+++ b/src/x64/code-stubs-x64.h
@@ -360,6 +360,7 @@ class RecordWriteStub: public PlatformCodeStub {
 };
 
 
-} }  // namespace v8::internal
+}  // namespace internal
+}  // namespace v8
 
 #endif  // V8_X64_CODE_STUBS_X64_H_