Make global variable gTimeDeltaForTesting lazily created.
Make global variable gTimeDeltaForTesting lazily created.

It's a fix for compilation error: "declaration requires a global constructor [-Werror,-Wglobal-constructors]"

BUG=

Review URL: https://codereview.chromium.org/1851443003

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#384724}

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