Fixup lint errors.

This CL fixes up the various lint errors.

Change-Id: If4d3077b55aadec33980452c43917194d803fac6
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/31680
Reviewed-by: Ben Clayton <bclayton@google.com>
Reviewed-by: Ryan Harrison <rharrison@chromium.org>
Commit-Queue: dan sinclair <dsinclair@chromium.org>

src/source.cc

@@ -12,9 +12,10 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-#include <sstream>
+#include "src/source.h"
 
-#include "source.h"
+#include <sstream>
+#include <utility>
 
 namespace tint {
 namespace {