DevTools: Fix members visibility in NetworkPanel.js

NetworkPanel.js is oversized (~3K lines) and contains multiple classes.
It is hard to navigate inside it.

I'm going to split it.

In this patch all visibility problems are addressed, so
split will not require additional code changes.

BUG=

Review URL: https://codereview.chromium.org/495533002

git-svn-id: svn://svn.chromium.org/blink/trunk@180769 bbb929c8-8fbe-4397-9dbb-9b2b20218538