DNR: Improve install warnings.

This CL improves the install warnings for manifest rules which can't be parsed.
To do this enable error generation for the Declarative Net Request API. Another
side effect of this is that rules with unknown keys are now ignored (with an
install warning), instead of being parsed correctly.

Generate code diff- https://www.diffchecker.com/9d55eAZ5

BUG=926609

Change-Id: I695225f8dd8e96366d6462d31414402d0b14c4f4
Reviewed-on: https://chromium-review.googlesource.com/c/1454085
Commit-Queue: Karan Bhatia <karandeepb@chromium.org>
Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#629788}
5 files changed