GitLab

 - Fixing almost all existing violations
   (remaining ones are fixed at crrev.com/2903063007).
 - Enabling http://eslint.org/docs/rules/semi check during PRESUBMIT

This enforces the following section from the styleguide:
https://google.github.io/styleguide/jsguide.html#formatting-semicolons-are-required

BUG=720034
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:closure_compilation

Review-Url: https://codereview.chromium.org/2909503003
Cr-Commit-Position: refs/heads/master@{#475771}