NOLINT a few operator overloads, to enable whitespace/operators

Review: https://reviews.apache.org/r/19967
Enabled whitespace/operators rule for cpplint.

Enabled whitespace/operators rule for cpplint, which covers the following:
You should always have whitespace around binary operators.
Missing spaces around <, >, or =
We allow no-spaces around << when used like this: 10<<20, but
not otherwise (particularly, not when used as streams)
There shouldn't be space around unary operators

Review: https://reviews.apache.org/r/19967