DevTools: Move HAREntry.js "sdk" -> "network"

Suggested by vsevik. This requires "extensions" to load the "network"
module for HAR operations.

R=pfeldman, vsevik

Review URL: https://codereview.chromium.org/302553003

git-svn-id: svn://svn.chromium.org/blink/trunk@174872 bbb929c8-8fbe-4397-9dbb-9b2b20218538