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Only WebSocket connections from the main page were tested. WebSocket connections
from Workers should also lead to display of an interstitial.

Modify malware_websocket.html to accept a "type" query parameter indicating
which environment to create the WebSocket in. Make the MalwareWebSocketBlocked
tests be parameterised on the environment type.

Due to a recent change (https://codereview.chromium.org/2960703003), these
changes need to be tested by passing --enable-features=NetworkService to
browser_tests, as opposed to the --enable-network-service argument that was
needed before.

BUG=644744

Review-Url: https://codereview.chromium.org/2971333002
Cr-Commit-Position: refs/heads/master@{#488151}