Add comments to QueryMetadata, minor style fixes.
Add comments to QueryMetadata, minor style fixes.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=146673830

angulardart/angular,matanlurey/angular,kevmoo/angular,chalin/angular2,chalin/angular2,chalin/angular2,kevmoo/angular,angulardart/angular,matanlurey/angular,kevmoo/angular,angulardart/angular,matanlurey/angular