`<link rel=preload>` with no `as` should be subject to connect-src
This CL aligns the implementation with the preload spec, so that fetches
triggered by link preload that has no `as` type, are subject to the
connect-src directive.
BUG=
580758
Committed:
https://crrev.com/33d50063a357635a3dbe9c4c880f39f2838fe0d8
Cr-Commit-Position: refs/heads/master@{#371491}