Remove connection paramter from all methods in ConnectionToClient::EventHandler

The connection parameter in ConnectionToClient::EventHandler is redundant
and can be removed.

Review-Url: https://codereview.chromium.org/2374593002
Cr-Commit-Position: refs/heads/master@{#421052}
11 files changed