Return const by ref instead of const by value in Issue:id()
Return const by ref instead of const by value in Issue:id()

BUG=393155

Review URL: https://codereview.chromium.org/1338713003

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#349213}

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