Averaging nested result lists instead of flattening them.
Averaging nested result lists instead of flattening them.

Also, removing special case where certain metrics where summed instead of averaged since they are now handled in the dashboard by averaging, no longer making them special cases.

BUG=447588

Review URL: https://codereview.chromium.org/847273002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#311377}

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