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It is not defined in implementation, and it is not needed to be checked.
https://chromium.googlesource.com/chromium/src/+/master/third_party/WebKit/Source/bindings/IDLExtendedAttributes.md#LogActivity_m_a

BUG=650150

Review-Url: https://codereview.chromium.org/2439413002
Cr-Commit-Position: refs/heads/master@{#427055}