Revert "Extensions: Make most of WebRequestInfo immutable."

This reverts commit ac4285c888b05e23c7fe1ffbef01130b3684121d.

Reason for revert: This CL probably broke Linux MSAN builds: 
https://ci.chromium.org/p/chromium/builders/ci/Linux%20MSan%20Tests/16666

Original change's description:
> Extensions: Make most of WebRequestInfo immutable.
> 
> This CL makes most of the WebRequestInfo data members const. To achieve this, a
> new helper struct called WebRequestInfoInitParams is introduced. This will help
> with guarantees around WebRequestInfo's immutability.
> 
> BUG=696822
> TBR=mmenke@chromium.org
> 
> Change-Id: I36bd8284aca9e68e115fba94b579456902f968ec
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1594066
> Commit-Queue: Karan Bhatia <karandeepb@chromium.org>
> Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#656970}

TBR=rdevlin.cronin@chromium.org,mmenke@chromium.org,karandeepb@chromium.org

Change-Id: I97b9b014a9e83aaff4ced979a99011f8593bd196
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 696822
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1599008
Reviewed-by: Christian Dullweber <dullweber@chromium.org>
Commit-Queue: Christian Dullweber <dullweber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#657178}
20 files changed