Assert non-null arguments in a few Closure DOM methods.
Assert non-null arguments in a few Closure DOM methods.

This is a small step towards being able to fix the nullability of our DOM externs. Note that the changed methods already crash on null arguments (either by trying to access a property, or by calling a DOM API which itself crashes on a null argument).

RELNOTES: n/a

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=214309555

teppeis/closure-library,google/closure-library,google/closure-library,google/closure-library,teppeis/closure-library,teppeis/closure-library,teppeis/closure-library,lucidsoftware/closure-library,google/closure-library,google/closure-library,lucidsoftware/closure-library,lucidsoftware/closure-library,lucidsoftware/closure-library