Add UseCounters for Selection methods that take null
Making collapse's argument non-nullable appears risky:
https://codereview.chromium.org/1498253002/#msg9
The risk for setBaseAndExtent is entirely unknown.
Measure both cases before proceeding further.
The change to Selection.idl is for clarity only, these are implicitly
nullable because of [LegacyInterfaceTypeChecking], and adding making
them explicitly nullable does not change the generated code.
Review URL: https://codereview.chromium.org/1509353004
Cr-Commit-Position: refs/heads/master@{#364344}
5 files changed
