Cleanup lint errors.

This CL cleans up some lint errors.

Change-Id: Ibfe9768cc4272d015a35a8d7edde0390b8fc66a5
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/19504
Reviewed-by: Ryan Harrison <rharrison@chromium.org>

src/ast/if_statement.h

@@ -1,4 +1,4 @@
-// Copyright 2020 The Tint Authors.
+// Copyright 2020 The Tint Authors.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.

src/ast/variable.h

@@ -1,4 +1,4 @@
-// Copyright 2020 The Tint Authors.
+// Copyright 2020 The Tint Authors.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.

src/reader/spirv/function.h

@@ -16,6 +16,8 @@
 #define SRC_READER_SPIRV_FUNCTION_H_
 
 #include <memory>
+#include <unordered_map>
+#include <unordered_set>
 #include <vector>
 
 #include "source/opt/basic_block.h"