Update WebCore.FeatureObserver histogram owner.
Update WebCore.FeatureObserver histogram owner.

R=asvitkine
BUG=

Review URL: https://codereview.chromium.org/1220063003

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#337234}

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