v8binding: Minor clean-up about EventListener::operator==

In general in C++, operator==(lhs, rhs) should be a global
function rather than a member function because
a) Member functions are easy to be asymmetric.
b) Virtual member functions are easier to be asymmetric.
c) It's hard to handle lhs=nullptr case.

This patch makes operator== a global function for
RegisteredEventListener class, also renames operator==
to 'Matches' for EventListener class.

Change-Id: I3e9d7dd4c1a5bd6e7d4186ec67541a42b05eb458
Reviewed-on: https://chromium-review.googlesource.com/c/1425061
Commit-Queue: Yuki Shiino <yukishiino@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Hitoshi Yoshida <peria@chromium.org>
Cr-Commit-Position: refs/heads/master@{#624767}
8 files changed